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https://github.com/PSI-Rockin/DobieStation.git
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131 lines
3.5 KiB
C
131 lines
3.5 KiB
C
/*
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* adler32.c - Adler-32 checksum algorithm
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*
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* Copyright 2016 Eric Biggers
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following
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* conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include "lib_common.h"
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#include "libdeflate.h"
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/* The Adler-32 divisor, or "base", value. */
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#define DIVISOR 65521
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/*
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* MAX_CHUNK_SIZE is the most bytes that can be processed without the
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* possibility of s2 overflowing when it is represented as an unsigned 32-bit
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* integer. This value was computed using the following Python script:
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*
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* divisor = 65521
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* count = 0
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* s1 = divisor - 1
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* s2 = divisor - 1
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* while True:
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* s1 += 0xFF
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* s2 += s1
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* if s2 > 0xFFFFFFFF:
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* break
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* count += 1
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* print(count)
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*
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* Note that to get the correct worst-case value, we must assume that every byte
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* has value 0xFF and that s1 and s2 started with the highest possible values
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* modulo the divisor.
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*/
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#define MAX_CHUNK_SIZE 5552
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typedef u32 (*adler32_func_t)(u32, const u8 *, size_t);
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/* Include architecture-specific implementations if available */
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#undef DEFAULT_IMPL
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#undef DISPATCH
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#if defined(__arm__) || defined(__aarch64__)
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# include "arm/adler32_impl.h"
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#elif defined(__i386__) || defined(__x86_64__)
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# include "x86/adler32_impl.h"
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#endif
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/* Define a generic implementation if needed */
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#ifndef DEFAULT_IMPL
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#define DEFAULT_IMPL adler32_generic
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static u32 adler32_generic(u32 adler, const u8 *p, size_t size)
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{
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u32 s1 = adler & 0xFFFF;
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u32 s2 = adler >> 16;
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const u8 * const end = p + size;
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while (p != end) {
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size_t chunk_size = MIN(end - p, MAX_CHUNK_SIZE);
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const u8 *chunk_end = p + chunk_size;
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size_t num_unrolled_iterations = chunk_size / 4;
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while (num_unrolled_iterations--) {
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s1 += *p++;
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s2 += s1;
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s1 += *p++;
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s2 += s1;
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s1 += *p++;
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s2 += s1;
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s1 += *p++;
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s2 += s1;
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}
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while (p != chunk_end) {
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s1 += *p++;
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s2 += s1;
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}
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s1 %= DIVISOR;
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s2 %= DIVISOR;
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}
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return (s2 << 16) | s1;
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}
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#endif /* !DEFAULT_IMPL */
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#ifdef DISPATCH
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static u32 dispatch(u32, const u8 *, size_t);
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static volatile adler32_func_t adler32_impl = dispatch;
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/* Choose the fastest implementation at runtime */
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static u32 dispatch(u32 adler, const u8 *buffer, size_t size)
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{
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adler32_func_t f = arch_select_adler32_func();
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if (f == NULL)
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f = DEFAULT_IMPL;
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adler32_impl = f;
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return adler32_impl(adler, buffer, size);
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}
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#else
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# define adler32_impl DEFAULT_IMPL /* only one implementation, use it */
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#endif
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LIBDEFLATEAPI u32
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libdeflate_adler32(u32 adler, const void *buffer, size_t size)
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{
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if (buffer == NULL) /* return initial value */
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return 1;
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return adler32_impl(adler, buffer, size);
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}
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