/* compare256_avx512.c -- AVX512 version of compare256

 * Copyright (C) 2025 Hans Kristian Rosbach

 * Based on AVX2 implementation by Mika T. Lindqvist

 * 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_AVX512) && defined(HAVE_BUILTIN_CTZLL)

#include <immintrin.h>

#ifdef _MSC_VER

#  include <nmmintrin.h>

#endif

static inline uint32_t compare256_avx512_static(const uint8_t *src0, const uint8_t *src1) {

    __m512i zmm_src0_4, zmm_src1_4;

    __m512i zmm_src0_3, zmm_src1_3;

    __m512i zmm_src0_2, zmm_src1_2;

    __m512i zmm_src0_1, zmm_src1_1;

    __m128i xmm_src0_0, xmm_src1_0;

    uint64_t mask_1, mask_2, mask_3, mask_4;

    uint32_t mask_0;

    // First do a 16byte round before increasing to 64bytes, this reduces the

    // penalty for the short matches, and those are usually the most common ones.

    // This requires us to overlap on the last round, giving a small penalty

    // on matches of 192+ bytes (Still faster than AVX2 though).

    // 16 bytes

    xmm_src0_0 = _mm_loadu_si128((__m128i*)src0);

    xmm_src1_0 = _mm_loadu_si128((__m128i*)src1);

    mask_0 = (uint32_t)_mm_cmpeq_epu8_mask(xmm_src0_0, xmm_src1_0); // zero-extended to use __builtin_ctz

    if (mask_0 != 0x0000FFFF) {

        // There is potential for using __builtin_ctzg/__builtin_ctzs/_tzcnt_u16/__tzcnt_u16 here

        uint32_t match_byte = (uint32_t)__builtin_ctz(~mask_0); /* Invert bits so identical = 0 */

        return match_byte;

    }

    // 64 bytes

    zmm_src0_1 = _mm512_loadu_si512((__m512i*)(src0 + 16));

    zmm_src1_1 = _mm512_loadu_si512((__m512i*)(src1 + 16));

    mask_1 = _mm512_cmpeq_epu8_mask(zmm_src0_1, zmm_src1_1);

    if (mask_1 != 0xFFFFFFFFFFFFFFFF) {

        uint32_t match_byte = (uint32_t)__builtin_ctzll(~mask_1);

        return 16 + match_byte;

    }

    // 64 bytes

    zmm_src0_2 = _mm512_loadu_si512((__m512i*)(src0 + 80));

    zmm_src1_2 = _mm512_loadu_si512((__m512i*)(src1 + 80));

    mask_2 = _mm512_cmpeq_epu8_mask(zmm_src0_2, zmm_src1_2);

    if (mask_2 != 0xFFFFFFFFFFFFFFFF) {

        uint32_t match_byte = (uint32_t)__builtin_ctzll(~mask_2);

        return 80 + match_byte;

    }

    // 64 bytes

    zmm_src0_3 = _mm512_loadu_si512((__m512i*)(src0 + 144));

    zmm_src1_3 = _mm512_loadu_si512((__m512i*)(src1 + 144));

    mask_3 = _mm512_cmpeq_epu8_mask(zmm_src0_3, zmm_src1_3);

    if (mask_3 != 0xFFFFFFFFFFFFFFFF) {

        uint32_t match_byte = (uint32_t)__builtin_ctzll(~mask_3);

        return 144 + match_byte;

    }

    // 64 bytes (overlaps the previous 16 bytes for fast tail processing)

    zmm_src0_4 = _mm512_loadu_si512((__m512i*)(src0 + 192));

    zmm_src1_4 = _mm512_loadu_si512((__m512i*)(src1 + 192));

    mask_4 = _mm512_cmpeq_epu8_mask(zmm_src0_4, zmm_src1_4);

    if (mask_4 != 0xFFFFFFFFFFFFFFFF) {

        uint32_t match_byte = (uint32_t)__builtin_ctzll(~mask_4);

        return 192 + match_byte;

    }

    return 256;

}

Z_INTERNAL uint32_t compare256_avx512(const uint8_t *src0, const uint8_t *src1) {

    return compare256_avx512_static(src0, src1);

}

#define LONGEST_MATCH       longest_match_avx512

#define COMPARE256          compare256_avx512_static

#include "match_tpl.h"

#define LONGEST_MATCH_SLOW

#define LONGEST_MATCH       longest_match_slow_avx512

#define COMPARE256          compare256_avx512_static

#include "match_tpl.h"

#endif