/* compare258.c -- aligned and unaligned versions of compare258
 * Copyright (C) 2020 Nathan Moinvaziri
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "zbuild.h"
#include "zutil.h"

#include "fallback_builtins.h"

/* ALIGNED, byte comparison */
static inline uint32_t compare256_c_static(const unsigned char *src0, const unsigned char *src1) {
    uint32_t len = 0;

    do {
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
        if (*src0 != *src1)
            return len + (*src0 == *src1);
        src0 += 1, src1 += 1, len += 1;
    } while (len < 256);

    return 256;
}

static inline uint32_t compare258_c_static(const unsigned char *src0, const unsigned char *src1) {
    if (*src0 != *src1)
        return 0;
    src0 += 1, src1 += 1;
    if (*src0 != *src1)
        return 1;
    src0 += 1, src1 += 1;

    return compare256_c_static(src0, src1) + 2;
}

Z_INTERNAL uint32_t compare258_c(const unsigned char *src0, const unsigned char *src1) {
    return compare258_c_static(src0, src1);
}

#define LONGEST_MATCH   longest_match_c
#define COMPARE256      compare256_c_static
#define COMPARE258      compare258_c_static

#include "match_tpl.h"

#ifdef UNALIGNED_OK
/* UNALIGNED_OK, 16-bit integer comparison */
static inline uint32_t compare256_unaligned_16_static(const unsigned char *src0, const unsigned char *src1) {
    uint32_t len = 0;

    do {
        if (*(uint16_t *)src0 != *(uint16_t *)src1)
            return len + (*src0 == *src1);
        src0 += 2, src1 += 2, len += 2;
        if (*(uint16_t *)src0 != *(uint16_t *)src1)
            return len + (*src0 == *src1);
        src0 += 2, src1 += 2, len += 2;
        if (*(uint16_t *)src0 != *(uint16_t *)src1)
            return len + (*src0 == *src1);
        src0 += 2, src1 += 2, len += 2;
        if (*(uint16_t *)src0 != *(uint16_t *)src1)
            return len + (*src0 == *src1);
        src0 += 2, src1 += 2, len += 2;
    } while (len < 256);

    return 256;
}

static inline uint32_t compare258_unaligned_16_static(const unsigned char *src0, const unsigned char *src1) {
    if (*(uint16_t *)src0 != *(uint16_t *)src1)
        return (*src0 == *src1);

    return compare256_unaligned_16_static(src0+2, src1+2) + 2;
}

Z_INTERNAL uint32_t compare258_unaligned_16(const unsigned char *src0, const unsigned char *src1) {
    return compare258_unaligned_16_static(src0, src1);
}

#define LONGEST_MATCH   longest_match_unaligned_16
#define COMPARE256      compare256_unaligned_16_static
#define COMPARE258      compare258_unaligned_16_static

#include "match_tpl.h"

#ifdef HAVE_BUILTIN_CTZ
/* UNALIGNED_OK, 32-bit integer comparison */
static inline uint32_t compare256_unaligned_32_static(const unsigned char *src0, const unsigned char *src1) {
    uint32_t len = 0;

    do {
        uint32_t sv = *(uint32_t *)src0;
        uint32_t mv = *(uint32_t *)src1;
        uint32_t diff = sv ^ mv;

        if (diff) {
            uint32_t match_byte = __builtin_ctz(diff) / 8;
            return len + match_byte;
        }

        src0 += 4, src1 += 4, len += 4;
    } while (len < 256);

    return 256;
}

static inline uint32_t compare258_unaligned_32_static(const unsigned char *src0, const unsigned char *src1) {
    if (*(uint16_t *)src0 != *(uint16_t *)src1)
        return (*src0 == *src1);

    return compare256_unaligned_32_static(src0+2, src1+2) + 2;
}

Z_INTERNAL uint32_t compare258_unaligned_32(const unsigned char *src0, const unsigned char *src1) {
    return compare258_unaligned_32_static(src0, src1);
}

#define LONGEST_MATCH   longest_match_unaligned_32
#define COMPARE256      compare256_unaligned_32_static
#define COMPARE258      compare258_unaligned_32_static

#include "match_tpl.h"

#endif

#if defined(UNALIGNED64_OK) && defined(HAVE_BUILTIN_CTZLL)
/* UNALIGNED64_OK, 64-bit integer comparison */
static inline uint32_t compare256_unaligned_64_static(const unsigned char *src0, const unsigned char *src1) {
    uint32_t len = 0;

    do {
        uint64_t sv = *(uint64_t *)src0;
        uint64_t mv = *(uint64_t *)src1;
        uint64_t diff = sv ^ mv;

        if (diff) {
            uint64_t match_byte = __builtin_ctzll(diff) / 8;
            return len + (uint32_t)match_byte;
        }

        src0 += 8, src1 += 8, len += 8;
    } while (len < 256);

    return 256;
}

static inline uint32_t compare258_unaligned_64_static(const unsigned char *src0, const unsigned char *src1) {
    if (*(uint16_t *)src0 != *(uint16_t *)src1)
        return (*src0 == *src1);

    return compare256_unaligned_64_static(src0+2, src1+2) + 2;
}

Z_INTERNAL uint32_t compare258_unaligned_64(const unsigned char *src0, const unsigned char *src1) {
    return compare258_unaligned_64_static(src0, src1);
}

#define LONGEST_MATCH   longest_match_unaligned_64
#define COMPARE256      compare256_unaligned_64_static
#define COMPARE258      compare258_unaligned_64_static

#include "match_tpl.h"

#endif

#endif