Index: src/core/SkChecksum.h |
diff --git a/src/core/SkChecksum.h b/src/core/SkChecksum.h |
deleted file mode 100644 |
index 8eb1766ec0c2639b23b3a7e29cac9b291d3340c4..0000000000000000000000000000000000000000 |
--- a/src/core/SkChecksum.h |
+++ /dev/null |
@@ -1,198 +0,0 @@ |
-/* |
- * Copyright 2012 Google Inc. |
- * |
- * Use of this source code is governed by a BSD-style license that can be |
- * found in the LICENSE file. |
- */ |
- |
-#ifndef SkChecksum_DEFINED |
-#define SkChecksum_DEFINED |
- |
-#include "SkString.h" |
-#include "SkTLogic.h" |
-#include "SkTypes.h" |
- |
-/** |
- * Computes a 32bit checksum from a blob of 32bit aligned data. This is meant |
- * to be very very fast, as it is used internally by the font cache, in |
- * conjuction with the entire raw key. This algorithm does not generate |
- * unique values as well as others (e.g. MD5) but it performs much faster. |
- * Skia's use cases can survive non-unique values (since the entire key is |
- * always available). Clients should only be used in circumstances where speed |
- * over uniqueness is at a premium. |
- */ |
-class SkChecksum : SkNoncopyable { |
-private: |
- /* |
- * Our Rotate and Mash helpers are meant to automatically do the right |
- * thing depending if sizeof(uintptr_t) is 4 or 8. |
- */ |
- enum { |
- ROTR = 17, |
- ROTL = sizeof(uintptr_t) * 8 - ROTR, |
- HALFBITS = sizeof(uintptr_t) * 4 |
- }; |
- |
- static inline uintptr_t Mash(uintptr_t total, uintptr_t value) { |
- return ((total >> ROTR) | (total << ROTL)) ^ value; |
- } |
- |
-public: |
- /** |
- * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you |
- * suspect its low bits aren't well mixed. |
- * |
- * This is the Murmur3 finalizer. |
- */ |
- static uint32_t Mix(uint32_t hash) { |
- hash ^= hash >> 16; |
- hash *= 0x85ebca6b; |
- hash ^= hash >> 13; |
- hash *= 0xc2b2ae35; |
- hash ^= hash >> 16; |
- return hash; |
- } |
- |
- /** |
- * uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you |
- * suspect its low bits aren't well mixed. |
- * |
- * This version is 2-lines cheaper than Mix, but seems to be sufficient for the font cache. |
- */ |
- static uint32_t CheapMix(uint32_t hash) { |
- hash ^= hash >> 16; |
- hash *= 0x85ebca6b; |
- hash ^= hash >> 16; |
- return hash; |
- } |
- |
- /** |
- * Calculate 32-bit Murmur hash (murmur3). |
- * This should take 2-3x longer than SkChecksum::Compute, but is a considerably better hash. |
- * See en.wikipedia.org/wiki/MurmurHash. |
- * |
- * @param data Memory address of the data block to be processed. |
- * @param size Size of the data block in bytes. |
- * @param seed Initial hash seed. (optional) |
- * @return hash result |
- */ |
- static uint32_t Murmur3(const void* data, size_t bytes, uint32_t seed=0) { |
- // Use may_alias to remind the compiler we're intentionally violating strict aliasing, |
- // and so not to apply strict-aliasing-based optimizations. |
- typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t; |
- typedef uint8_t SK_ATTRIBUTE(may_alias) aliased_uint8_t; |
- |
- // Handle 4 bytes at a time while possible. |
- const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data; |
- const size_t words = bytes/4; |
- uint32_t hash = seed; |
- for (size_t i = 0; i < words; i++) { |
- uint32_t k = safe_data[i]; |
- k *= 0xcc9e2d51; |
- k = (k << 15) | (k >> 17); |
- k *= 0x1b873593; |
- |
- hash ^= k; |
- hash = (hash << 13) | (hash >> 19); |
- hash *= 5; |
- hash += 0xe6546b64; |
- } |
- |
- // Handle last 0-3 bytes. |
- const aliased_uint8_t* safe_tail = (const uint8_t*)(safe_data + words); |
- uint32_t k = 0; |
- switch (bytes & 3) { |
- case 3: k ^= safe_tail[2] << 16; |
- case 2: k ^= safe_tail[1] << 8; |
- case 1: k ^= safe_tail[0] << 0; |
- k *= 0xcc9e2d51; |
- k = (k << 15) | (k >> 17); |
- k *= 0x1b873593; |
- hash ^= k; |
- } |
- |
- hash ^= bytes; |
- return Mix(hash); |
- } |
- |
- /** |
- * Compute a 32-bit checksum for a given data block |
- * |
- * WARNING: this algorithm is tuned for efficiency, not backward/forward |
- * compatibility. It may change at any time, so a checksum generated with |
- * one version of the Skia code may not match a checksum generated with |
- * a different version of the Skia code. |
- * |
- * @param data Memory address of the data block to be processed. Must be |
- * 32-bit aligned. |
- * @param size Size of the data block in bytes. Must be a multiple of 4. |
- * @return checksum result |
- */ |
- static uint32_t Compute(const uint32_t* data, size_t size) { |
- // Use may_alias to remind the compiler we're intentionally violating strict aliasing, |
- // and so not to apply strict-aliasing-based optimizations. |
- typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t; |
- const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data; |
- |
- SkASSERT(SkIsAlign4(size)); |
- |
- /* |
- * We want to let the compiler use 32bit or 64bit addressing and math |
- * so we use uintptr_t as our magic type. This makes the code a little |
- * more obscure (we can't hard-code 32 or 64 anywhere, but have to use |
- * sizeof()). |
- */ |
- uintptr_t result = 0; |
- const uintptr_t* ptr = reinterpret_cast<const uintptr_t*>(safe_data); |
- |
- /* |
- * count the number of quad element chunks. This takes into account |
- * if we're on a 32bit or 64bit arch, since we use sizeof(uintptr_t) |
- * to compute how much to shift-down the size. |
- */ |
- size_t n4 = size / (sizeof(uintptr_t) << 2); |
- for (size_t i = 0; i < n4; ++i) { |
- result = Mash(result, *ptr++); |
- result = Mash(result, *ptr++); |
- result = Mash(result, *ptr++); |
- result = Mash(result, *ptr++); |
- } |
- size &= ((sizeof(uintptr_t) << 2) - 1); |
- |
- safe_data = reinterpret_cast<const aliased_uint32_t*>(ptr); |
- const aliased_uint32_t* stop = safe_data + (size >> 2); |
- while (safe_data < stop) { |
- result = Mash(result, *safe_data++); |
- } |
- |
- /* |
- * smash us down to 32bits if we were 64. Note that when uintptr_t is |
- * 32bits, this code-path should go away, but I still got a warning |
- * when I wrote |
- * result ^= result >> 32; |
- * since >>32 is undefined for 32bit ints, hence the wacky HALFBITS |
- * define. |
- */ |
- if (8 == sizeof(result)) { |
- result ^= result >> HALFBITS; |
- } |
- return static_cast<uint32_t>(result); |
- } |
-}; |
- |
-// SkGoodHash should usually be your first choice in hashing data. |
-// It should be both reasonably fast and high quality. |
- |
-template <typename K> |
-uint32_t SkGoodHash(const K& k) { |
- if (sizeof(K) == 4) { |
- return SkChecksum::Mix(*(const uint32_t*)&k); |
- } |
- return SkChecksum::Murmur3(&k, sizeof(K)); |
-} |
- |
-inline uint32_t SkGoodHash(const SkString& k) { |
- return SkChecksum::Murmur3(k.c_str(), k.size()); |
-} |
- |
-#endif |