diff options
author | reed@google.com <reed@google.com@2bbb7eff-a529-9590-31e7-b0007b416f81> | 2012-07-03 19:44:20 +0000 |
---|---|---|
committer | reed@google.com <reed@google.com@2bbb7eff-a529-9590-31e7-b0007b416f81> | 2012-07-03 19:44:20 +0000 |
commit | 88db9ef0cd8646171f35a3325706291070b5dc55 (patch) | |
tree | bac1288c36ee57bf9ac9ec83eaa9339654e1b7cb /include/core/SkChecksum.h | |
parent | 54823c227d383308fb1732e83b566df6272d4bfb (diff) |
add SkChecksum as a static class, for the replacement API
after this lands, plan to deprecate/remove the older APIs
Review URL: https://codereview.appspot.com/6356059
git-svn-id: http://skia.googlecode.com/svn/trunk@4457 2bbb7eff-a529-9590-31e7-b0007b416f81
Diffstat (limited to 'include/core/SkChecksum.h')
-rw-r--r-- | include/core/SkChecksum.h | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/include/core/SkChecksum.h b/include/core/SkChecksum.h index ab88cbc01a..e8117f9b12 100644 --- a/include/core/SkChecksum.h +++ b/include/core/SkChecksum.h @@ -67,5 +67,78 @@ inline uint32_t SkComputeChecksum32(const uint32_t* ptr, size_t size) { } return result; } + +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: + /** + * Compute a 32-bit checksum for a given data block + * + * @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) { + 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*>(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. + */ + int n4 = size / (sizeof(uintptr_t) << 2); + for (int 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); + + data = reinterpret_cast<const uint32_t*>(ptr); + const uint32_t* stop = data + (size >> 2); + while (data < stop) { + result = Mash(result, *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); + } +}; + #endif |