1ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org/* 2ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org * Copyright 2012 Google Inc. 3ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org * 4ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org * Use of this source code is governed by a BSD-style license that can be 5ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org * found in the LICENSE file. 6ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org */ 7ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org 8ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org#ifndef SkChecksum_DEFINED 9ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org#define SkChecksum_DEFINED 10ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org 11ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org#include "SkTypes.h" 12ef76060cbf36032a5bef9cd8d18138704349c3aejunov@chromium.org 13d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com/** 14d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * Computes a 32bit checksum from a blob of 32bit aligned data. This is meant 15d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * to be very very fast, as it is used internally by the font cache, in 16d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * conjuction with the entire raw key. This algorithm does not generate 17d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * unique values as well as others (e.g. MD5) but it performs much faster. 18d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * Skia's use cases can survive non-unique values (since the entire key is 19d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * always available). Clients should only be used in circumstances where speed 20d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com * over uniqueness is at a premium. 21d42f7587e5972d7e787b5cf2a043c33fbe96091freed@google.com */ 2288db9ef0cd8646171f35a3325706291070b5dc55reed@google.comclass SkChecksum : SkNoncopyable { 2388db9ef0cd8646171f35a3325706291070b5dc55reed@google.comprivate: 2488db9ef0cd8646171f35a3325706291070b5dc55reed@google.com /* 2588db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * Our Rotate and Mash helpers are meant to automatically do the right 2688db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * thing depending if sizeof(uintptr_t) is 4 or 8. 2788db9ef0cd8646171f35a3325706291070b5dc55reed@google.com */ 2888db9ef0cd8646171f35a3325706291070b5dc55reed@google.com enum { 2988db9ef0cd8646171f35a3325706291070b5dc55reed@google.com ROTR = 17, 3088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com ROTL = sizeof(uintptr_t) * 8 - ROTR, 3188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com HALFBITS = sizeof(uintptr_t) * 4 3288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com }; 33fbfcd5602128ec010c82cb733c9cdc0a3254f9f3rmistry@google.com 3488db9ef0cd8646171f35a3325706291070b5dc55reed@google.com static inline uintptr_t Mash(uintptr_t total, uintptr_t value) { 3588db9ef0cd8646171f35a3325706291070b5dc55reed@google.com return ((total >> ROTR) | (total << ROTL)) ^ value; 3688db9ef0cd8646171f35a3325706291070b5dc55reed@google.com } 37fbfcd5602128ec010c82cb733c9cdc0a3254f9f3rmistry@google.com 3888db9ef0cd8646171f35a3325706291070b5dc55reed@google.compublic: 3967a3271f0de9ccc32d559b042b862528272047ccmtklein /** 4067a3271f0de9ccc32d559b042b862528272047ccmtklein * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you 4167a3271f0de9ccc32d559b042b862528272047ccmtklein * suspect its low bits aren't well mixed. 4267a3271f0de9ccc32d559b042b862528272047ccmtklein * 4367a3271f0de9ccc32d559b042b862528272047ccmtklein * This is the Murmur3 finalizer. 4467a3271f0de9ccc32d559b042b862528272047ccmtklein */ 4567a3271f0de9ccc32d559b042b862528272047ccmtklein static uint32_t Mix(uint32_t hash) { 4667a3271f0de9ccc32d559b042b862528272047ccmtklein hash ^= hash >> 16; 4767a3271f0de9ccc32d559b042b862528272047ccmtklein hash *= 0x85ebca6b; 4867a3271f0de9ccc32d559b042b862528272047ccmtklein hash ^= hash >> 13; 4967a3271f0de9ccc32d559b042b862528272047ccmtklein hash *= 0xc2b2ae35; 5067a3271f0de9ccc32d559b042b862528272047ccmtklein hash ^= hash >> 16; 5167a3271f0de9ccc32d559b042b862528272047ccmtklein return hash; 5267a3271f0de9ccc32d559b042b862528272047ccmtklein } 5370d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org 5470d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org /** 5570d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * Calculate 32-bit Murmur hash (murmur3). 5670d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * This should take 2-3x longer than SkChecksum::Compute, but is a considerably better hash. 5770d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * See en.wikipedia.org/wiki/MurmurHash. 5870d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * 5970d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * @param data Memory address of the data block to be processed. Must be 32-bit aligned. 6070d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * @param size Size of the data block in bytes. Must be a multiple of 4. 6170d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * @param seed Initial hash seed. (optional) 6270d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org * @return hash result 6370d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org */ 64bbf9f6d1cbb94d3486072228781f6e3b6e2252e4reed static uint32_t Murmur3(const uint32_t* data, size_t bytes, uint32_t seed=0) { 6519fcc7494e68843cb9f2de819a7287ee216e3c5emtklein // Use may_alias to remind the compiler we're intentionally violating strict aliasing, 6619fcc7494e68843cb9f2de819a7287ee216e3c5emtklein // and so not to apply strict-aliasing-based optimizations. 6719fcc7494e68843cb9f2de819a7287ee216e3c5emtklein typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t; 6819fcc7494e68843cb9f2de819a7287ee216e3c5emtklein const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data; 6919fcc7494e68843cb9f2de819a7287ee216e3c5emtklein 7067a3271f0de9ccc32d559b042b862528272047ccmtklein SkASSERTF(SkIsAlign4(bytes), "Expected 4-byte multiple, got %zu", bytes); 7170d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org const size_t words = bytes/4; 7270d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org 7319fcc7494e68843cb9f2de819a7287ee216e3c5emtklein 7470d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org uint32_t hash = seed; 7570d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org for (size_t i = 0; i < words; i++) { 7619fcc7494e68843cb9f2de819a7287ee216e3c5emtklein uint32_t k = safe_data[i]; 7770d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org k *= 0xcc9e2d51; 7870d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org k = (k << 15) | (k >> 17); 7970d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org k *= 0x1b873593; 8070d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org 8170d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org hash ^= k; 8270d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org hash = (hash << 13) | (hash >> 19); 8370d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org hash *= 5; 8470d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org hash += 0xe6546b64; 8570d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org } 8670d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org hash ^= bytes; 8767a3271f0de9ccc32d559b042b862528272047ccmtklein return Mix(hash); 8870d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org } 8970d75ca764e16e15f016e423b85a0fa2a29fb8c7commit-bot@chromium.org 9088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com /** 9188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * Compute a 32-bit checksum for a given data block 9288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * 9341d0d2f9059bb72d8f4fab3b69bb15a17ea5dcb0epoger@google.com * WARNING: this algorithm is tuned for efficiency, not backward/forward 9441d0d2f9059bb72d8f4fab3b69bb15a17ea5dcb0epoger@google.com * compatibility. It may change at any time, so a checksum generated with 9541d0d2f9059bb72d8f4fab3b69bb15a17ea5dcb0epoger@google.com * one version of the Skia code may not match a checksum generated with 9641d0d2f9059bb72d8f4fab3b69bb15a17ea5dcb0epoger@google.com * a different version of the Skia code. 9741d0d2f9059bb72d8f4fab3b69bb15a17ea5dcb0epoger@google.com * 9888db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * @param data Memory address of the data block to be processed. Must be 9988db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * 32-bit aligned. 10088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * @param size Size of the data block in bytes. Must be a multiple of 4. 10188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * @return checksum result 10288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com */ 103bbf9f6d1cbb94d3486072228781f6e3b6e2252e4reed static uint32_t Compute(const uint32_t* data, size_t size) { 10419fcc7494e68843cb9f2de819a7287ee216e3c5emtklein // Use may_alias to remind the compiler we're intentionally violating strict aliasing, 10519fcc7494e68843cb9f2de819a7287ee216e3c5emtklein // and so not to apply strict-aliasing-based optimizations. 10619fcc7494e68843cb9f2de819a7287ee216e3c5emtklein typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t; 10719fcc7494e68843cb9f2de819a7287ee216e3c5emtklein const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data; 10819fcc7494e68843cb9f2de819a7287ee216e3c5emtklein 10988db9ef0cd8646171f35a3325706291070b5dc55reed@google.com SkASSERT(SkIsAlign4(size)); 110fbfcd5602128ec010c82cb733c9cdc0a3254f9f3rmistry@google.com 11188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com /* 11288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * We want to let the compiler use 32bit or 64bit addressing and math 11388db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * so we use uintptr_t as our magic type. This makes the code a little 11488db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * more obscure (we can't hard-code 32 or 64 anywhere, but have to use 11588db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * sizeof()). 11688db9ef0cd8646171f35a3325706291070b5dc55reed@google.com */ 11788db9ef0cd8646171f35a3325706291070b5dc55reed@google.com uintptr_t result = 0; 11819fcc7494e68843cb9f2de819a7287ee216e3c5emtklein const uintptr_t* ptr = reinterpret_cast<const uintptr_t*>(safe_data); 119fbfcd5602128ec010c82cb733c9cdc0a3254f9f3rmistry@google.com 12088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com /* 12188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * count the number of quad element chunks. This takes into account 12288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * if we're on a 32bit or 64bit arch, since we use sizeof(uintptr_t) 12388db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * to compute how much to shift-down the size. 12488db9ef0cd8646171f35a3325706291070b5dc55reed@google.com */ 125b158a82bc18b5535224e3ca315ee6d80c7ad899breed@google.com size_t n4 = size / (sizeof(uintptr_t) << 2); 126b158a82bc18b5535224e3ca315ee6d80c7ad899breed@google.com for (size_t i = 0; i < n4; ++i) { 12788db9ef0cd8646171f35a3325706291070b5dc55reed@google.com result = Mash(result, *ptr++); 12888db9ef0cd8646171f35a3325706291070b5dc55reed@google.com result = Mash(result, *ptr++); 12988db9ef0cd8646171f35a3325706291070b5dc55reed@google.com result = Mash(result, *ptr++); 13088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com result = Mash(result, *ptr++); 13188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com } 13288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com size &= ((sizeof(uintptr_t) << 2) - 1); 133fbfcd5602128ec010c82cb733c9cdc0a3254f9f3rmistry@google.com 13419fcc7494e68843cb9f2de819a7287ee216e3c5emtklein safe_data = reinterpret_cast<const aliased_uint32_t*>(ptr); 13519fcc7494e68843cb9f2de819a7287ee216e3c5emtklein const aliased_uint32_t* stop = safe_data + (size >> 2); 13619fcc7494e68843cb9f2de819a7287ee216e3c5emtklein while (safe_data < stop) { 13719fcc7494e68843cb9f2de819a7287ee216e3c5emtklein result = Mash(result, *safe_data++); 13888db9ef0cd8646171f35a3325706291070b5dc55reed@google.com } 139fbfcd5602128ec010c82cb733c9cdc0a3254f9f3rmistry@google.com 14088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com /* 14188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * smash us down to 32bits if we were 64. Note that when uintptr_t is 14288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * 32bits, this code-path should go away, but I still got a warning 14388db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * when I wrote 14488db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * result ^= result >> 32; 14588db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * since >>32 is undefined for 32bit ints, hence the wacky HALFBITS 14688db9ef0cd8646171f35a3325706291070b5dc55reed@google.com * define. 14788db9ef0cd8646171f35a3325706291070b5dc55reed@google.com */ 14888db9ef0cd8646171f35a3325706291070b5dc55reed@google.com if (8 == sizeof(result)) { 14988db9ef0cd8646171f35a3325706291070b5dc55reed@google.com result ^= result >> HALFBITS; 15088db9ef0cd8646171f35a3325706291070b5dc55reed@google.com } 15188db9ef0cd8646171f35a3325706291070b5dc55reed@google.com return static_cast<uint32_t>(result); 15288db9ef0cd8646171f35a3325706291070b5dc55reed@google.com } 15388db9ef0cd8646171f35a3325706291070b5dc55reed@google.com}; 15488db9ef0cd8646171f35a3325706291070b5dc55reed@google.com 155fffc8d01b5fca2b2cfc40661c1ff4fdc7a0f9aecrobertphillips@google.com#endif 156