/* compare256_rle.h -- 256 byte run-length encoding comparison

 * Copyright (C) 2022 Nathan Moinvaziri

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

 */

#include "zbuild.h"

#include "zendian.h"

#include "zmemory.h"

#include "fallback_builtins.h"

typedef uint32_t (*compare256_rle_func)(const uint8_t* src0, const uint8_t* src1);

/* 8-bit RLE comparison for hardware without unaligned loads */

static inline uint32_t compare256_rle_8(const uint8_t *src0, const uint8_t *src1) {

    uint32_t len = 0;

    uint8_t val = *src0;

    do {

        if (val != src1[0])

            return len;

        if (val != src1[1])

            return len + 1;

        if (val != src1[2])

            return len + 2;

        if (val != src1[3])

            return len + 3;

        if (val != src1[4])

            return len + 4;

        if (val != src1[5])

            return len + 5;

        if (val != src1[6])

            return len + 6;

        if (val != src1[7])

            return len + 7;

        src1 += 8, len += 8;

    } while (len < 256);

    return 256;

}

/* 64-bit RLE comparison for hardware with unaligned loads */

static inline uint32_t compare256_rle_64(const uint8_t *src0, const uint8_t *src1) {

    uint32_t src0_cmp32, len = 0;

    uint16_t src0_cmp;

    uint64_t sv, mv, diff;

    src0_cmp = zng_memread_2(src0);

    src0_cmp32 = ((uint32_t)src0_cmp << 16) | src0_cmp;

    sv = ((uint64_t)src0_cmp32 << 32) | src0_cmp32;

    do {

        mv = zng_memread_8(src1);

        diff = sv ^ mv;

        if (diff)

            return len + zng_ctz64(Z_U64_TO_LE(diff)) / 8;

        src1 += 8, len += 8;

    } while (len < 256);

    return 256;

}