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Unified Diff: src/core/SkChecksum.h

Issue 1260613006: Move SkTHash.h to include/private. (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: rm Created 5 years, 5 months ago
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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
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