/* compare256_sse2.c -- SSE2 version of compare256

 * Copyright Adam Stylinski <kungfujesus06@gmail.com>

 * For conditions of distribution and use, see copyright notice in zlib.h

 */

#include "zbuild.h"

#include "zmemory.h"

#include "deflate.h"

#include "fallback_builtins.h"

#if defined(X86_SSE2) && defined(HAVE_BUILTIN_CTZ)

#include <emmintrin.h>

static inline uint32_t compare256_sse2_static(const uint8_t *src0, const uint8_t *src1) {

    uint32_t len = 0;

    int align_offset = ((uintptr_t)src0) & 15;

    const uint8_t *end0 = src0 + 256;

    const uint8_t *end1 = src1 + 256;

    __m128i xmm_src0, xmm_src1, xmm_cmp;

    /* Do the first load unaligned, than all subsequent ones we have at least

     * one aligned load. Sadly aligning both loads is probably unrealistic */

    xmm_src0 = _mm_loadu_si128((__m128i*)src0);

    xmm_src1 = _mm_loadu_si128((__m128i*)src1);

    xmm_cmp = _mm_cmpeq_epi8(xmm_src0, xmm_src1);

    unsigned mask = (unsigned)_mm_movemask_epi8(xmm_cmp);

    /* Compiler _may_ turn this branch into a ptest + movemask,

     * since a lot of those uops are shared and fused */

    if (mask != 0xFFFF) {

        uint32_t match_byte = (uint32_t)__builtin_ctz(~mask);

        return len + match_byte;

    }

    int align_adv = 16 - align_offset;

    len += align_adv;

    src0 += align_adv;

    src1 += align_adv;

    /* Do a flooring division (should just be a shift right) */

    int num_iter = (256 - len) / 16;

    for (int i = 0; i < num_iter; ++i) {

        xmm_src0 = _mm_load_si128((__m128i*)src0);

        xmm_src1 = _mm_loadu_si128((__m128i*)src1);

        xmm_cmp = _mm_cmpeq_epi8(xmm_src0, xmm_src1);

        mask = (unsigned)_mm_movemask_epi8(xmm_cmp);

        /* Compiler _may_ turn this branch into a ptest + movemask,

         * since a lot of those uops are shared and fused */

        if (mask != 0xFFFF) {

            uint32_t match_byte = (uint32_t)__builtin_ctz(~mask);

            return len + match_byte;

        }

        len += 16, src0 += 16, src1 += 16;

    }

    if (align_offset) {

        src0 = end0 - 16;

        src1 = end1 - 16;

        len = 256 - 16;

        xmm_src0 = _mm_loadu_si128((__m128i*)src0);

        xmm_src1 = _mm_loadu_si128((__m128i*)src1);

        xmm_cmp = _mm_cmpeq_epi8(xmm_src0, xmm_src1);

        mask = (unsigned)_mm_movemask_epi8(xmm_cmp);

        if (mask != 0xFFFF) {

            uint32_t match_byte = (uint32_t)__builtin_ctz(~mask);

            return len + match_byte;

        }

    }

    return 256;

}

Z_INTERNAL uint32_t compare256_sse2(const uint8_t *src0, const uint8_t *src1) {

    return compare256_sse2_static(src0, src1);

}

#define LONGEST_MATCH       longest_match_sse2

#define COMPARE256          compare256_sse2_static

#include "match_tpl.h"

#define LONGEST_MATCH_SLOW

#define LONGEST_MATCH       longest_match_slow_sse2

#define COMPARE256          compare256_sse2_static

#include "match_tpl.h"

#endif