/* * Copyright (c) 2008 Apple Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this * file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_LICENSE_HEADER_END@ */ /* Portions derived from: -------------------------------------------------------------------- lookup8.c, by Bob Jenkins, January 4 1997, Public Domain. hash(), hash2(), hash3, and mix() are externally useful functions. Routines to test the hash are included if SELF_TEST is defined. You can use this free for any purpose. It has no warranty. -------------------------------------------------------------------- ------------------------------------------------------------------------------ perfect.c: code to generate code for a hash for perfect hashing. (c) Bob Jenkins, September 1996, December 1999 You may use this code in any way you wish, and it is free. No warranty. I hereby place this in the public domain. Source is http://burtleburtle.net/bob/c/perfect.c ------------------------------------------------------------------------------ */ /* * objc-selopt.h * Interface between libobjc and dyld * for selector uniquing in the dyld shared cache. * * When building the shared cache, dyld locates all selectors and selector * references in the cached images. It builds a perfect hash table out of * them and writes the table into the shared cache copy of libobjc. * libobjc then uses that table as the builtin selector list. * * Versioning * The table has a version number. dyld and objc can both ignore the table * if the other used the wrong version number. * * Completeness * Not all libraries are in the shared cache. Libraries that are in the * shared cache and were optimized are specially marked. Libraries on * disk never include those marks. * * Coherency * Libraries optimized in the shared cache can be replaced by unoptimized * copies from disk when loaded. The copy from disk is not marked and will * be fixed up by libobjc. The shared cache copy is still mapped into the * process, so the table can point to cstring data in that library's part * of the shared cache without trouble. * * Atomicity * dyld writes the table itself last. If dyld marks some metadata as * updated but then fails to write a table for some reason, libobjc * fixes up all metadata as if it were not marked. */ #ifndef _OBJC_SELOPT_H #define _OBJC_SELOPT_H /* DO NOT INCLUDE ANY objc HEADERS HERE dyld USES THIS FILE AND CANNOT SEE THEM */ #include #include #ifdef SELOPT_WRITE #include #endif /* DO NOT INCLUDE ANY objc HEADERS HERE dyld USES THIS FILE AND CANNOT SEE THEM */ #ifndef STATIC_ASSERT # define STATIC_ASSERT(x) _STATIC_ASSERT2(x, __LINE__) # define _STATIC_ASSERT2(x, line) _STATIC_ASSERT3(x, line) # define _STATIC_ASSERT3(x, line) \ typedef struct { \ int _static_assert[(x) ? 0 : -1]; \ } _static_assert_ ## line __attribute__((unavailable)) #endif #define SELOPT_DEBUG 0 #define S32(x) x = little_endian ? OSSwapHostToLittleInt32(x) : OSSwapHostToBigInt32(x) #define S64(x) x = little_endian ? OSSwapHostToLittleInt64(x) : OSSwapHostToBigInt64(x) namespace objc_opt { typedef int32_t objc_stringhash_offset_t; typedef uint8_t objc_stringhash_check_t; static uint64_t lookup8( uint8_t *k, size_t length, uint64_t level); #ifdef SELOPT_WRITE // Perfect hash code is at the end of this file. struct __attribute__((packed)) perfect_hash { uint32_t capacity; uint32_t occupied; uint32_t shift; uint32_t mask; uint64_t salt; uint32_t scramble[256]; uint8_t *tab; // count == mask+1; free with delete[] perfect_hash() : tab(0) { } ~perfect_hash() { if (tab) delete[] tab; } }; struct eqstr { bool operator()(const char* s1, const char* s2) const { return strcmp(s1, s2) == 0; } }; struct hashstr { size_t operator()(const char *s) const { return (size_t)lookup8((uint8_t *)s, strlen(s), 0); } }; // cstring => cstring's vmaddress // (used for selector names and class names) typedef std::unordered_map string_map; // protocol name => protocol vmaddress typedef std::unordered_map protocol_map; // class name => (class vmaddress, header_info vmaddress) typedef std::unordered_multimap, hashstr, eqstr> class_map; static perfect_hash make_perfect(const string_map& strings); #endif // Precomputed perfect hash table of strings. // Base class for precomputed selector table and class table. // Edit objc-sel-table.s if you change this structure. struct __attribute__((packed)) objc_stringhash_t { uint32_t capacity; uint32_t occupied; uint32_t shift; uint32_t mask; uint32_t unused1; // was zero uint32_t unused2; // alignment pad uint64_t salt; uint32_t scramble[256]; uint8_t tab[0]; /* tab[mask+1] (always power-of-2) */ // uint8_t checkbytes[capacity]; /* check byte for each string */ // int32_t offsets[capacity]; /* offsets from &capacity to cstrings */ objc_stringhash_check_t *checkbytes() { return (objc_stringhash_check_t *)&tab[mask+1]; } const objc_stringhash_check_t *checkbytes() const { return (const objc_stringhash_check_t *)&tab[mask+1]; } objc_stringhash_offset_t *offsets() { return (objc_stringhash_offset_t *)&checkbytes()[capacity]; } const objc_stringhash_offset_t *offsets() const { return (const objc_stringhash_offset_t *)&checkbytes()[capacity]; } uint32_t hash(const char *key, size_t keylen) const { uint64_t val = lookup8((uint8_t*)key, keylen, salt); uint32_t index = (uint32_t)(val>>shift) ^ scramble[tab[val&mask]]; return index; } uint32_t hash(const char *key) const { return hash(key, strlen(key)); } // The check bytes areused to reject strings that aren't in the table // without paging in the table's cstring data. This checkbyte calculation // catches 4785/4815 rejects when launching Safari; a perfect checkbyte // would catch 4796/4815. objc_stringhash_check_t checkbyte(const char *key, size_t keylen) const { return ((key[0] & 0x7) << 5) | ((uint8_t)keylen & 0x1f); } objc_stringhash_check_t checkbyte(const char *key) const { return checkbyte(key, strlen(key)); } #define INDEX_NOT_FOUND (~(uint32_t)0) uint32_t getIndex(const char *key) const { size_t keylen = strlen(key); uint32_t h = hash(key, keylen); // Use check byte to reject without paging in the table's cstrings objc_stringhash_check_t h_check = checkbytes()[h]; objc_stringhash_check_t key_check = checkbyte(key, keylen); bool check_fail = (h_check != key_check); #if ! SELOPT_DEBUG if (check_fail) return INDEX_NOT_FOUND; #endif objc_stringhash_offset_t offset = offsets()[h]; if (offset == 0) return INDEX_NOT_FOUND; const char *result = (const char *)this + offset; if (0 != strcmp(key, result)) return INDEX_NOT_FOUND; #if SELOPT_DEBUG if (check_fail) abort(); #endif return h; } #ifdef SELOPT_WRITE size_t size() { return sizeof(objc_stringhash_t) + mask+1 + capacity * sizeof(objc_stringhash_check_t) + capacity * sizeof(objc_stringhash_offset_t); } void byteswap(bool little_endian) { // tab and checkbytes are arrays of bytes, no swap needed for (uint32_t i = 0; i < 256; i++) { S32(scramble[i]); } objc_stringhash_offset_t *o = offsets(); for (uint32_t i = 0; i < capacity; i++) { S32(o[i]); } S32(capacity); S32(occupied); S32(shift); S32(mask); S64(salt); } const char *write(uint64_t base, size_t remaining, string_map& strings) { if (sizeof(objc_stringhash_t) > remaining) { return "selector section too small (metadata not optimized)"; } if (strings.size() == 0) { bzero(this, sizeof(objc_stringhash_t)); return NULL; } perfect_hash phash = make_perfect(strings); if (phash.capacity == 0) { return "perfect hash failed (metadata not optimized)"; } // Set header capacity = phash.capacity; occupied = phash.occupied; shift = phash.shift; mask = phash.mask; unused1 = 0; unused2 = 0; salt = phash.salt; if (size() > remaining) { return "selector section too small (metadata not optimized)"; } // Set hash data for (uint32_t i = 0; i < 256; i++) { scramble[i] = phash.scramble[i]; } for (uint32_t i = 0; i < phash.mask+1; i++) { tab[i] = phash.tab[i]; } // Set offsets to 0 for (uint32_t i = 0; i < phash.capacity; i++) { offsets()[i] = 0; } // Set checkbytes to 0 for (uint32_t i = 0; i < phash.capacity; i++) { checkbytes()[i] = 0; } // Set real string offsets and checkbytes # define SHIFT (64 - 8*sizeof(objc_stringhash_offset_t)) string_map::const_iterator s; for (s = strings.begin(); s != strings.end(); ++s) { int64_t offset = s->second - base; if ((offset<>SHIFT != offset) { return "selector offset too big (metadata not optimized)"; } uint32_t h = hash(s->first); offsets()[h] = (objc_stringhash_offset_t)offset; checkbytes()[h] = checkbyte(s->first); } # undef SHIFT return NULL; } // SELOPT_WRITE #endif }; // Precomputed selector table. // Edit objc-sel-table.s if you change this structure. struct objc_selopt_t : objc_stringhash_t { const char *get(const char *key) const { uint32_t h = getIndex(key); if (h == INDEX_NOT_FOUND) return NULL; return (const char *)this + offsets()[h]; } }; // Precomputed class list. // Edit objc-sel-table.s if you change these structures. struct objc_classheader_t { objc_stringhash_offset_t clsOffset; objc_stringhash_offset_t hiOffset; // For duplicate class names: // clsOffset = count<<1 | 1 // duplicated classes are duplicateOffsets[hiOffset..hiOffset+count-1] bool isDuplicate() const { return clsOffset & 1; } uint32_t duplicateCount() const { return clsOffset >> 1; } uint32_t duplicateIndex() const { return hiOffset; } }; struct objc_clsopt_t : objc_stringhash_t { // ...objc_stringhash_t fields... // objc_classheader_t classOffsets[capacity]; /* offsets from &capacity to class_t and header_info */ // uint32_t duplicateCount; // objc_classheader_t duplicateOffsets[duplicatedClasses]; objc_classheader_t *classOffsets() { return (objc_classheader_t *)&offsets()[capacity]; } const objc_classheader_t *classOffsets() const { return (const objc_classheader_t *)&offsets()[capacity]; } uint32_t& duplicateCount() { return *(uint32_t *)&classOffsets()[capacity]; } const uint32_t& duplicateCount() const { return *(const uint32_t *)&classOffsets()[capacity]; } objc_classheader_t *duplicateOffsets() { return (objc_classheader_t *)(&duplicateCount()+1); } const objc_classheader_t *duplicateOffsets() const { return (const objc_classheader_t *)(&duplicateCount()+1); } // 0/NULL/NULL: not found // 1/ptr/ptr: found exactly one // n/NULL/NULL: found N - use getClassesAndHeaders() instead uint32_t getClassAndHeader(const char *key, void*& cls, void*& hi) const { uint32_t h = getIndex(key); if (h == INDEX_NOT_FOUND) { cls = NULL; hi = NULL; return 0; } const objc_classheader_t& clshi = classOffsets()[h]; if (! clshi.isDuplicate()) { // class appears in exactly one header cls = (void *)((const char *)this + clshi.clsOffset); hi = (void *)((const char *)this + clshi.hiOffset); return 1; } else { // class appears in more than one header - use getClassesAndHeaders cls = NULL; hi = NULL; return clshi.duplicateCount(); } } void getClassesAndHeaders(const char *key, void **cls, void **hi) const { uint32_t h = getIndex(key); if (h == INDEX_NOT_FOUND) return; const objc_classheader_t& clshi = classOffsets()[h]; if (! clshi.isDuplicate()) { // class appears in exactly one header cls[0] = (void *)((const char *)this + clshi.clsOffset); hi[0] = (void *)((const char *)this + clshi.hiOffset); } else { // class appears in more than one header uint32_t count = clshi.duplicateCount(); const objc_classheader_t *list = &duplicateOffsets()[clshi.duplicateIndex()]; for (uint32_t i = 0; i < count; i++) { cls[i] = (void *)((const char *)this + list[i].clsOffset); hi[i] = (void *)((const char *)this + list[i].hiOffset); } } } #ifdef SELOPT_WRITE size_t size() { return objc_stringhash_t::size() + capacity * sizeof(objc_classheader_t) + sizeof(duplicateCount()) + duplicateCount() * sizeof(objc_classheader_t); } void byteswap(bool little_endian) { objc_classheader_t *o; o = classOffsets(); for (uint32_t i = 0; i < capacity; i++) { S32(o[i].clsOffset); S32(o[i].hiOffset); } o = duplicateOffsets(); for (uint32_t i = 0; i < duplicateCount(); i++) { S32(o[i].clsOffset); S32(o[i].hiOffset); } S32(duplicateCount()); objc_stringhash_t::byteswap(little_endian); } const char *write(uint64_t base, size_t remaining, string_map& strings, class_map& classes, bool verbose) { const char *err; err = objc_stringhash_t::write(base, remaining, strings); if (err) return err; if (size() > remaining) { return "selector section too small (metadata not optimized)"; } // Set class offsets to 0 for (uint32_t i = 0; i < capacity; i++) { classOffsets()[i].clsOffset = 0; classOffsets()[i].hiOffset = 0; } // Set real class offsets # define SHIFT (64 - 8*sizeof(objc_stringhash_offset_t)) class_map::const_iterator c; for (c = classes.begin(); c != classes.end(); ++c) { uint32_t h = getIndex(c->first); if (h == INDEX_NOT_FOUND) { return "class list busted (metadata not optimized)"; } if (classOffsets()[h].clsOffset != 0) { // already did this class continue; } uint32_t count = (uint32_t)classes.count(c->first); if (count == 1) { // only one class with this name int64_t coff = c->second.first - base; int64_t hoff = c->second.second - base; if ((coff<>SHIFT != coff) { return "class offset too big (metadata not optimized)"; } if ((hoff<>SHIFT != hoff) { return "header offset too big (metadata not optimized)"; } classOffsets()[h].clsOffset = (objc_stringhash_offset_t)coff; classOffsets()[h].hiOffset = (objc_stringhash_offset_t)hoff; } else { // class name has duplicates - write them all now if (verbose) { fprintf(stderr, "update_dyld_shared_cache: %u duplicates of Objective-C class %s\n", count, c->first); } uint32_t dest = duplicateCount(); duplicateCount() += count; if (size() > remaining) { return "selector section too small (metadata not optimized)"; } // classOffsets() instead contains count and array index classOffsets()[h].clsOffset = count*2 + 1; classOffsets()[h].hiOffset = dest; std::pair duplicates = classes.equal_range(c->first); class_map::const_iterator dup; for (dup = duplicates.first; dup != duplicates.second; ++dup) { int64_t coff = dup->second.first - base; int64_t hoff = dup->second.second - base; if ((coff<>SHIFT != coff) { return "class offset too big (metadata not optimized)"; } if ((hoff<>SHIFT != hoff) { return "header offset too big (metadata not optimized)"; } duplicateOffsets()[dest].clsOffset = (objc_stringhash_offset_t)coff; duplicateOffsets()[dest].hiOffset = (objc_stringhash_offset_t)hoff; dest++; } } } # undef SHIFT return NULL; } // SELOPT_WRITE #endif }; struct objc_protocolopt_t : objc_stringhash_t { // ...objc_stringhash_t fields... // uint32_t protocolOffsets[capacity]; /* offsets from &capacity to protocol_t */ objc_stringhash_offset_t *protocolOffsets() { return (objc_stringhash_offset_t *)&offsets()[capacity]; } const objc_stringhash_offset_t *protocolOffsets() const { return (const objc_stringhash_offset_t *)&offsets()[capacity]; } void* getProtocol(const char *key) const { uint32_t h = getIndex(key); if (h == INDEX_NOT_FOUND) { return NULL; } return (void *)((const char *)this + protocolOffsets()[h]); } #ifdef SELOPT_WRITE size_t size() { return objc_stringhash_t::size() + capacity * sizeof(objc_stringhash_offset_t); } void byteswap(bool little_endian) { objc_stringhash_offset_t *o; o = protocolOffsets(); for (objc_stringhash_offset_t i = 0; i < (int)capacity; i++) { S32(o[i]); } objc_stringhash_t::byteswap(little_endian); } const char *write(uint64_t base, size_t remaining, string_map& strings, protocol_map& protocols, bool verbose) { const char *err; err = objc_stringhash_t::write(base, remaining, strings); if (err) return err; if (size() > remaining) { return "selector section too small (metadata not optimized)"; } // Set protocol offsets to 0 for (uint32_t i = 0; i < capacity; i++) { protocolOffsets()[i] = 0; } // Set real protocol offsets # define SHIFT (64 - 8*sizeof(objc_stringhash_offset_t)) protocol_map::const_iterator c; for (c = protocols.begin(); c != protocols.end(); ++c) { uint32_t h = getIndex(c->first); if (h == INDEX_NOT_FOUND) { return "protocol list busted (metadata not optimized)"; } int64_t offset = c->second - base; if ((offset<>SHIFT != offset) { return "protocol offset too big (metadata not optimized)"; } protocolOffsets()[h] = (objc_stringhash_offset_t)offset; } # undef SHIFT return NULL; } // SELOPT_WRITE #endif }; // Precomputed image list. struct objc_headeropt_ro_t; // Precomputed image list. struct objc_headeropt_rw_t; // Precomputed class list. struct objc_clsopt_t; // Edit objc-sel-table.s if you change this value. // lldb and Symbolication read these structures. Inform them of any changes. enum { VERSION = 15 }; // Values for objc_opt_t::flags enum : uint32_t { IsProduction = (1 << 0), // never set in development cache NoMissingWeakSuperclasses = (1 << 1), // never set in development cache }; // Top-level optimization structure. // Edit objc-sel-table.s if you change this structure. struct alignas(alignof(void*)) objc_opt_t { uint32_t version; uint32_t flags; int32_t selopt_offset; int32_t headeropt_ro_offset; int32_t clsopt_offset; int32_t protocolopt_offset; int32_t headeropt_rw_offset; const objc_selopt_t* selopt() const { if (selopt_offset == 0) return NULL; return (objc_selopt_t *)((uint8_t *)this + selopt_offset); } objc_selopt_t* selopt() { if (selopt_offset == 0) return NULL; return (objc_selopt_t *)((uint8_t *)this + selopt_offset); } struct objc_headeropt_ro_t* headeropt_ro() const { if (headeropt_ro_offset == 0) return NULL; return (struct objc_headeropt_ro_t *)((uint8_t *)this + headeropt_ro_offset); } struct objc_clsopt_t* clsopt() const { if (clsopt_offset == 0) return NULL; return (objc_clsopt_t *)((uint8_t *)this + clsopt_offset); } struct objc_protocolopt_t* protocolopt() const { if (protocolopt_offset == 0) return NULL; return (objc_protocolopt_t *)((uint8_t *)this + protocolopt_offset); } struct objc_headeropt_rw_t* headeropt_rw() const { if (headeropt_rw_offset == 0) return NULL; return (struct objc_headeropt_rw_t *)((uint8_t *)this + headeropt_rw_offset); } }; // sizeof(objc_opt_t) must be pointer-aligned STATIC_ASSERT(sizeof(objc_opt_t) % sizeof(void*) == 0); // List of offsets in libobjc that the shared cache optimization needs to use. template struct objc_opt_pointerlist_tt { T protocolClass; }; typedef struct objc_opt_pointerlist_tt objc_opt_pointerlist_t; /* -------------------------------------------------------------------- mix -- mix 3 64-bit values reversibly. mix() takes 48 machine instructions, but only 24 cycles on a superscalar machine (like Intel's new MMX architecture). It requires 4 64-bit registers for 4::2 parallelism. All 1-bit deltas, all 2-bit deltas, all deltas composed of top bits of (a,b,c), and all deltas of bottom bits were tested. All deltas were tested both on random keys and on keys that were nearly all zero. These deltas all cause every bit of c to change between 1/3 and 2/3 of the time (well, only 113/400 to 287/400 of the time for some 2-bit delta). These deltas all cause at least 80 bits to change among (a,b,c) when the mix is run either forward or backward (yes it is reversible). This implies that a hash using mix64 has no funnels. There may be characteristics with 3-bit deltas or bigger, I didn't test for those. -------------------------------------------------------------------- */ #define mix64(a,b,c) \ { \ a -= b; a -= c; a ^= (c>>43); \ b -= c; b -= a; b ^= (a<<9); \ c -= a; c -= b; c ^= (b>>8); \ a -= b; a -= c; a ^= (c>>38); \ b -= c; b -= a; b ^= (a<<23); \ c -= a; c -= b; c ^= (b>>5); \ a -= b; a -= c; a ^= (c>>35); \ b -= c; b -= a; b ^= (a<<49); \ c -= a; c -= b; c ^= (b>>11); \ a -= b; a -= c; a ^= (c>>12); \ b -= c; b -= a; b ^= (a<<18); \ c -= a; c -= b; c ^= (b>>22); \ } /* -------------------------------------------------------------------- hash() -- hash a variable-length key into a 64-bit value k : the key (the unaligned variable-length array of bytes) len : the length of the key, counting by bytes level : can be any 8-byte value Returns a 64-bit value. Every bit of the key affects every bit of the return value. No funnels. Every 1-bit and 2-bit delta achieves avalanche. About 41+5len instructions. The best hash table sizes are powers of 2. There is no need to do mod a prime (mod is sooo slow!). If you need less than 64 bits, use a bitmask. For example, if you need only 10 bits, do h = (h & hashmask(10)); In which case, the hash table should have hashsize(10) elements. If you are hashing n strings (uint8_t **)k, do it like this: for (i=0, h=0; i= 24) { a += (k[0] +((uint64_t)k[ 1]<< 8)+((uint64_t)k[ 2]<<16)+((uint64_t)k[ 3]<<24) +((uint64_t)k[4 ]<<32)+((uint64_t)k[ 5]<<40)+((uint64_t)k[ 6]<<48)+((uint64_t)k[ 7]<<56)); b += (k[8] +((uint64_t)k[ 9]<< 8)+((uint64_t)k[10]<<16)+((uint64_t)k[11]<<24) +((uint64_t)k[12]<<32)+((uint64_t)k[13]<<40)+((uint64_t)k[14]<<48)+((uint64_t)k[15]<<56)); c += (k[16] +((uint64_t)k[17]<< 8)+((uint64_t)k[18]<<16)+((uint64_t)k[19]<<24) +((uint64_t)k[20]<<32)+((uint64_t)k[21]<<40)+((uint64_t)k[22]<<48)+((uint64_t)k[23]<<56)); mix64(a,b,c); k += 24; len -= 24; } /*------------------------------------- handle the last 23 bytes */ c += length; switch(len) /* all the case statements fall through */ { case 23: c+=((uint64_t)k[22]<<56); case 22: c+=((uint64_t)k[21]<<48); case 21: c+=((uint64_t)k[20]<<40); case 20: c+=((uint64_t)k[19]<<32); case 19: c+=((uint64_t)k[18]<<24); case 18: c+=((uint64_t)k[17]<<16); case 17: c+=((uint64_t)k[16]<<8); /* the first byte of c is reserved for the length */ case 16: b+=((uint64_t)k[15]<<56); case 15: b+=((uint64_t)k[14]<<48); case 14: b+=((uint64_t)k[13]<<40); case 13: b+=((uint64_t)k[12]<<32); case 12: b+=((uint64_t)k[11]<<24); case 11: b+=((uint64_t)k[10]<<16); case 10: b+=((uint64_t)k[ 9]<<8); case 9: b+=((uint64_t)k[ 8]); case 8: a+=((uint64_t)k[ 7]<<56); case 7: a+=((uint64_t)k[ 6]<<48); case 6: a+=((uint64_t)k[ 5]<<40); case 5: a+=((uint64_t)k[ 4]<<32); case 4: a+=((uint64_t)k[ 3]<<24); case 3: a+=((uint64_t)k[ 2]<<16); case 2: a+=((uint64_t)k[ 1]<<8); case 1: a+=((uint64_t)k[ 0]); /* case 0: nothing left to add */ } mix64(a,b,c); /*-------------------------------------------- report the result */ return c; } #ifdef SELOPT_WRITE /* ------------------------------------------------------------------------------ This generates a minimal perfect hash function. That means, given a set of n keys, this determines a hash function that maps each of those keys into a value in 0..n-1 with no collisions. The perfect hash function first uses a normal hash function on the key to determine (a,b) such that the pair (a,b) is distinct for all keys, then it computes a^scramble[tab[b]] to get the final perfect hash. tab[] is an array of 1-byte values and scramble[] is a 256-term array of 2-byte or 4-byte values. If there are n keys, the length of tab[] is a power of two between n/3 and n. I found the idea of computing distinct (a,b) values in "Practical minimal perfect hash functions for large databases", Fox, Heath, Chen, and Daoud, Communications of the ACM, January 1992. They found the idea in Chichelli (CACM Jan 1980). Beyond that, our methods differ. The key is hashed to a pair (a,b) where a in 0..*alen*-1 and b in 0..*blen*-1. A fast hash function determines both a and b simultaneously. Any decent hash function is likely to produce hashes so that (a,b) is distinct for all pairs. I try the hash using different values of *salt* until all pairs are distinct. The final hash is (a XOR scramble[tab[b]]). *scramble* is a predetermined mapping of 0..255 into 0..smax-1. *tab* is an array that we fill in in such a way as to make the hash perfect. First we fill in all values of *tab* that are used by more than one key. We try all possible values for each position until one works. This leaves m unmapped keys and m values that something could hash to. If you treat unmapped keys as lefthand nodes and unused hash values as righthand nodes, and draw a line connecting each key to each hash value it could map to, you get a bipartite graph. We attempt to find a perfect matching in this graph. If we succeed, we have determined a perfect hash for the whole set of keys. *scramble* is used because (a^tab[i]) clusters keys around *a*. ------------------------------------------------------------------------------ */ typedef uint64_t ub8; #define UB8MAXVAL 0xffffffffffffffffLL #define UB8BITS 64 typedef uint32_t ub4; #define UB4MAXVAL 0xffffffff #define UB4BITS 32 typedef uint16_t ub2; #define UB2MAXVAL 0xffff #define UB2BITS 16 typedef uint8_t ub1; #define UB1MAXVAL 0xff #define UB1BITS 8 #define TRUE 1 #define FALSE 0 #define SCRAMBLE_LEN 256 // ((ub4)1<<16) /* length of *scramble* */ #define RETRY_INITKEY 2048 /* number of times to try to find distinct (a,b) */ #define RETRY_PERFECT 4 /* number of times to try to make a perfect hash */ /* representation of a key */ struct key { ub1 *name_k; /* the actual key */ ub4 len_k; /* the length of the actual key */ ub4 hash_k; /* the initial hash value for this key */ /* beyond this point is mapping-dependent */ ub4 a_k; /* a, of the key maps to (a,b) */ ub4 b_k; /* b, of the key maps to (a,b) */ struct key *nextb_k; /* next key with this b */ }; typedef struct key key; /* things indexed by b of original (a,b) pair */ struct bstuff { ub2 val_b; /* hash=a^tabb[b].val_b */ key *list_b; /* tabb[i].list_b is list of keys with b==i */ ub4 listlen_b; /* length of list_b */ ub4 water_b; /* high watermark of who has visited this map node */ }; typedef struct bstuff bstuff; /* things indexed by final hash value */ struct hstuff { key *key_h; /* tabh[i].key_h is the key with a hash of i */ }; typedef struct hstuff hstuff; /* things indexed by queue position */ struct qstuff { bstuff *b_q; /* b that currently occupies this hash */ ub4 parent_q; /* queue position of parent that could use this hash */ ub2 newval_q; /* what to change parent tab[b] to to use this hash */ ub2 oldval_q; /* original value of tab[b] */ }; typedef struct qstuff qstuff; /* ------------------------------------------------------------------------------ Find the mapping that will produce a perfect hash ------------------------------------------------------------------------------ */ /* return the ceiling of the log (base 2) of val */ static ub4 log2u(ub4 val) { ub4 i; for (i=0; ((ub4)1<>const3)); x = (x+(x<>const5)); } return x; } /* initialize scramble[] with distinct random values in 0..smax-1 */ static void scrambleinit(ub4 *scramble, ub4 smax) // ub4 *scramble; /* hash is a^scramble[tab[b]] */ // ub4 smax; /* scramble values should be in 0..smax-1 */ { ub4 i; /* fill scramble[] with distinct random integers in 0..smax-1 */ for (i=0; ib_k * check if the initial hash might work */ static int inittab(bstuff *tabb, ub4 blen, key *keys, ub4 nkeys, int complete) // bstuff *tabb; /* output, list of keys with b for (a,b) */ // ub4 blen; /* length of tabb */ // key *keys; /* list of keys already hashed */ // int complete; /* TRUE means to complete init despite collisions */ { int nocollision = TRUE; ub4 i; memset((void *)tabb, 0, (size_t)(sizeof(bstuff)*blen)); /* Two keys with the same (a,b) guarantees a collision */ for (i = 0; i < nkeys; i++) { key *mykey = keys+i; key *otherkey; for (otherkey=tabb[mykey->b_k].list_b; otherkey; otherkey=otherkey->nextb_k) { if (mykey->a_k == otherkey->a_k) { nocollision = FALSE; if (!complete) return FALSE; } } ++tabb[mykey->b_k].listlen_b; mykey->nextb_k = tabb[mykey->b_k].list_b; tabb[mykey->b_k].list_b = mykey; } /* no two keys have the same (a,b) pair */ return nocollision; } /* Do the initial hash for normal mode (use lookup and checksum) */ static void initnorm(key *keys, ub4 nkeys, ub4 alen, ub4 blen, ub4 smax, ub8 salt) // key *keys; /* list of all keys */ // ub4 alen; /* (a,b) has a in 0..alen-1, a power of 2 */ // ub4 blen; /* (a,b) has b in 0..blen-1, a power of 2 */ // ub4 smax; /* maximum range of computable hash values */ // ub4 salt; /* used to initialize the hash function */ // gencode *final; /* output, code for the final hash */ { ub4 loga = log2u(alen); /* log based 2 of blen */ dispatch_apply(nkeys, DISPATCH_APPLY_AUTO, ^(size_t index) { ub4 i = (ub4)index; key *mykey = keys+i; ub8 hash = lookup8(mykey->name_k, mykey->len_k, salt); mykey->a_k = (loga > 0) ? (ub4)(hash >> (UB8BITS-loga)) : 0; mykey->b_k = (blen > 1) ? (hash & (blen-1)) : 0; }); } /* Try to apply an augmenting list */ static int apply(bstuff *tabb, hstuff *tabh, qstuff *tabq, ub4 blen, ub4 *scramble, ub4 tail, int rollback) // bstuff *tabb; // hstuff *tabh; // qstuff *tabq; // ub4 blen; // ub4 *scramble; // ub4 tail; // int rollback; /* FALSE applies augmenting path, TRUE rolls back */ { ub4 hash; key *mykey; bstuff *pb; ub4 child; ub4 parent; ub4 stabb; /* scramble[tab[b]] */ /* walk from child to parent */ for (child=tail-1; child; child=parent) { parent = tabq[child].parent_q; /* find child's parent */ pb = tabq[parent].b_q; /* find parent's list of siblings */ /* erase old hash values */ stabb = scramble[pb->val_b]; for (mykey=pb->list_b; mykey; mykey=mykey->nextb_k) { hash = mykey->a_k^stabb; if (mykey == tabh[hash].key_h) { /* erase hash for all of child's siblings */ tabh[hash].key_h = (key *)0; } } /* change pb->val_b, which will change the hashes of all parent siblings */ pb->val_b = (rollback ? tabq[child].oldval_q : tabq[child].newval_q); /* set new hash values */ stabb = scramble[pb->val_b]; for (mykey=pb->list_b; mykey; mykey=mykey->nextb_k) { hash = mykey->a_k^stabb; if (rollback) { if (parent == 0) continue; /* root never had a hash */ } else if (tabh[hash].key_h) { /* very rare: roll back any changes */ apply(tabb, tabh, tabq, blen, scramble, tail, TRUE); return FALSE; /* failure, collision */ } tabh[hash].key_h = mykey; } } return TRUE; } /* ------------------------------------------------------------------------------- augment(): Add item to the mapping. Construct a spanning tree of *b*s with *item* as root, where each parent can have all its hashes changed (by some new val_b) with at most one collision, and each child is the b of that collision. I got this from Tarjan's "Data Structures and Network Algorithms". The path from *item* to a *b* that can be remapped with no collision is an "augmenting path". Change values of tab[b] along the path so that the unmapped key gets mapped and the unused hash value gets used. Assuming 1 key per b, if m out of n hash values are still unused, you should expect the transitive closure to cover n/m nodes before an unused node is found. Sum(i=1..n)(n/i) is about nlogn, so expect this approach to take about nlogn time to map all single-key b's. ------------------------------------------------------------------------------- */ static int augment(bstuff *tabb, hstuff *tabh, qstuff *tabq, ub4 blen, ub4 *scramble, ub4 smax, bstuff *item, ub4 nkeys, ub4 highwater) // bstuff *tabb; /* stuff indexed by b */ // hstuff *tabh; /* which key is associated with which hash, indexed by hash */ // qstuff *tabq; /* queue of *b* values, this is the spanning tree */ // ub4 blen; /* length of tabb */ // ub4 *scramble; /* final hash is a^scramble[tab[b]] */ // ub4 smax; /* highest value in scramble */ // bstuff *item; /* &tabb[b] for the b to be mapped */ // ub4 nkeys; /* final hash must be in 0..nkeys-1 */ // ub4 highwater; /* a value higher than any now in tabb[].water_b */ { ub4 q; /* current position walking through the queue */ ub4 tail; /* tail of the queue. 0 is the head of the queue. */ ub4 limit=UB1MAXVAL+1; ub4 highhash = smax; /* initialize the root of the spanning tree */ tabq[0].b_q = item; tail = 1; /* construct the spanning tree by walking the queue, add children to tail */ for (q=0; qval_b */ if (q == 1) break; /* don't do transitive closure */ for (i=0; ilist_b; mykey; mykey=mykey->nextb_k) { key *childkey; ub4 hash = mykey->a_k^scramble[i]; if (hash >= highhash) break; /* out of bounds */ childkey = tabh[hash].key_h; if (childkey) { bstuff *hitb = &tabb[childkey->b_k]; if (childb) { if (childb != hitb) break; /* hit at most one child b */ } else { childb = hitb; /* remember this as childb */ if (childb->water_b == highwater) break; /* already explored */ } } } if (mykey) continue; /* myb with i has multiple collisions */ /* add childb to the queue of reachable things */ if (childb) childb->water_b = highwater; tabq[tail].b_q = childb; tabq[tail].newval_q = i; /* how to make parent (myb) use this hash */ tabq[tail].oldval_q = myb->val_b; /* need this for rollback */ tabq[tail].parent_q = q; ++tail; if (!childb) { /* found an *i* with no collisions? */ /* try to apply the augmenting path */ if (apply(tabb, tabh, tabq, blen, scramble, tail, FALSE)) return TRUE; /* success, item was added to the perfect hash */ --tail; /* don't know how to handle such a child! */ } } } return FALSE; } /* find a mapping that makes this a perfect hash */ static int perfect(bstuff *tabb, hstuff *tabh, qstuff *tabq, ub4 blen, ub4 smax, ub4 *scramble, ub4 nkeys) { ub4 maxkeys; /* maximum number of keys for any b */ ub4 i, j; #if SELOPT_DEBUG fprintf(stderr, " blen %d smax %d nkeys %d\n", blen, smax, nkeys); #endif /* clear any state from previous attempts */ memset((void *)tabh, 0, sizeof(hstuff)*smax); memset((void *)tabq, 0, sizeof(qstuff)*(blen+1)); for (maxkeys=0,i=0; i maxkeys) maxkeys = tabb[i].listlen_b; /* In descending order by number of keys, map all *b*s */ for (j=maxkeys; j>0; --j) for (i=0; i= RETRY_INITKEY) { /* Try to put more bits in (A,B) to make distinct (A,B) more likely */ if (*alen < maxalen) { *alen *= 2; } else if (*blen < smax) { *blen *= 2; delete[] tabq; delete[] *tabb; *tabb = new bstuff[*blen]; tabq = new qstuff[*blen+1]; } bad_initkey = 0; bad_perfect = 0; } continue; /* two keys have same (a,b) pair */ } /* Given distinct (A,B) for all keys, build a perfect hash */ if (!perfect(*tabb, tabh, tabq, *blen, smax, scramble, nkeys)) { if (++bad_perfect >= RETRY_PERFECT) { if (*blen < smax) { *blen *= 2; delete[] *tabb; delete[] tabq; *tabb = new bstuff[*blen]; tabq = new qstuff[*blen+1]; --si; /* we know this salt got distinct (A,B) */ } else { return 0; } bad_perfect = 0; } continue; } break; } /* free working memory */ delete[] tabh; delete[] tabq; return 1; } /* ------------------------------------------------------------------------------ Input/output type routines ------------------------------------------------------------------------------ */ /* get the list of keys */ static void getkeys(key **keys, ub4 *nkeys, const string_map& strings) { key *buf = new key[strings.size()]; size_t i; string_map::const_iterator s; for (i = 0, s = strings.begin(); s != strings.end(); ++s, ++i) { key *mykey = buf+i; mykey->name_k = (ub1 *)s->first; mykey->len_k = (ub4)strlen(s->first); } *keys = buf; *nkeys = (ub4)strings.size(); } static perfect_hash make_perfect(const string_map& strings) { ub4 nkeys; /* number of keys */ key *keys; /* head of list of keys */ bstuff *tab; /* table indexed by b */ ub4 smax; /* scramble[] values in 0..smax-1, a power of 2 */ ub4 alen; /* a in 0..alen-1, a power of 2 */ ub4 blen; /* b in 0..blen-1, a power of 2 */ ub8 salt; /* a parameter to the hash function */ ub4 scramble[SCRAMBLE_LEN]; /* used in final hash function */ int ok; uint32_t i; perfect_hash result; /* read in the list of keywords */ getkeys(&keys, &nkeys, strings); /* find the hash */ smax = ((ub4)1<