%---------------------------------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et
%---------------------------------------------------------------------------%
% Copyright (C) 2021, 2023, 2025 The Mercury team.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%---------------------------------------------------------------------------%
%
% File: md5.m.
% Main author: wangp.
%
% This module contains an implementation of the MD5 message digest algorithm.
%
%---------------------------------------------------------------------------%

:- module libs.md5.
:- interface.

:- func md5sum(string) = string.

%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%

:- implementation.

:- import_module require.   % Required by non-C grades.

%---------------------------------------------------------------------------%

/*
 * This is an OpenSSL-compatible implementation of the RSA Data Security, Inc.
 * MD5 Message-Digest Algorithm (RFC 1321).
 *
 * Homepage:
 * http://openwall.info/wiki/people/solar/software/
 *  public-domain-source-code/md5
 *
 * Author:
 * Alexander Peslyak, better known as Solar Designer <solar at openwall.com>
 *
 * This software was written by Alexander Peslyak in 2001.  No copyright is
 * claimed, and the software is hereby placed in the public domain.
 * In case this attempt to disclaim copyright and place the software in the
 * public domain is deemed null and void, then the software is
 * Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
 * general public under the following terms:
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted.
 *
 * There's ABSOLUTELY NO WARRANTY, express or implied.
 *
 * (This is a heavily cut-down "BSD license".)
 *
 * This differs from Colin Plumb's older public domain implementation in that
 * no exactly 32-bit integer data type is required (any 32-bit or wider
 * unsigned integer data type will do), there's no compile-time endianness
 * configuration, and the function prototypes match OpenSSL's.  No code from
 * Colin Plumb's implementation has been reused; this comment merely compares
 * the properties of the two independent implementations.
 *
 * The primary goals of this implementation are portability and ease of use.
 * It is meant to be fast, but not as fast as possible.  Some known
 * optimizations are not included to reduce source code size and avoid
 * compile-time configuration.
 */

:- pragma foreign_decl("C", "local", "
/* Any 32-bit or wider unsigned integer data type will do */
typedef MR_uint_least32_t MD5_u32plus;

typedef struct {
    MD5_u32plus lo, hi;
    MD5_u32plus a, b, c, d;
    unsigned char buffer[64];
    MD5_u32plus block[16];
} MD5_CTX;

static void MD5_Init(MD5_CTX *ctx);
static void MD5_Update(MD5_CTX *ctx, const void *data, unsigned long size);
static void MD5_Final(unsigned char *result, MD5_CTX *ctx);
").

:- pragma foreign_code("C", "
/*
 * The basic MD5 functions.
 *
 * F and G are optimized compared to their RFC 1321 definitions for
 * architectures that lack an AND-NOT instruction, just like in Colin Plumb's
 * implementation.
 */
#define F(x, y, z)          ((z) ^ ((x) & ((y) ^ (z))))
#define G(x, y, z)          ((y) ^ ((z) & ((x) ^ (y))))
#define H(x, y, z)          (((x) ^ (y)) ^ (z))
#define H2(x, y, z)         ((x) ^ ((y) ^ (z)))
#define I(x, y, z)          ((y) ^ ((x) | ~(z)))

/*
 * The MD5 transformation for all four rounds.
 */
#define STEP(f, a, b, c, d, x, t, s) \
    (a) += f((b), (c), (d)) + (x) + (t); \
    (a) = (((a) << (s)) | (((a) & 0xffffffff) >> (32 - (s)))); \
    (a) += (b);

/*
 * SET reads 4 input bytes in little-endian byte order and stores them in a
 * properly aligned word in host byte order.
 *
 * The check for little-endian architectures that tolerate unaligned memory
 * accesses is just an optimization.  Nothing will break if it fails to detect
 * a suitable architecture.
 *
 * Unfortunately, this optimization may be a C strict aliasing rules violation
 * if the caller's data buffer has effective type that cannot be aliased by
 * MD5_u32plus.  In practice, this problem may occur if these MD5 routines are
 * inlined into a calling function, or with future and dangerously advanced
 * link-time optimizations.  For the time being, keeping these MD5 routines in
 * their own translation unit avoids the problem.
 */
#if defined(__i386__) || defined(__x86_64__) || defined(__vax__)
#define SET(n) \
    (*(MD5_u32plus *)&ptr[(n) * 4])
#define GET(n) \
    SET(n)
#else
#define SET(n) \
    (ctx->block[(n)] = \
    (MD5_u32plus)ptr[(n) * 4] | \
    ((MD5_u32plus)ptr[(n) * 4 + 1] << 8) | \
    ((MD5_u32plus)ptr[(n) * 4 + 2] << 16) | \
    ((MD5_u32plus)ptr[(n) * 4 + 3] << 24))
#define GET(n) \
    (ctx->block[(n)])
#endif

/*
 * This processes one or more 64-byte data blocks, but does NOT update the bit
 * counters.  There are no alignment requirements.
 */
static const void *body(MD5_CTX *ctx, const void *data, unsigned long size)
{
    const unsigned char *ptr;
    MD5_u32plus a, b, c, d;
    MD5_u32plus saved_a, saved_b, saved_c, saved_d;

    ptr = (const unsigned char *)data;

    a = ctx->a;
    b = ctx->b;
    c = ctx->c;
    d = ctx->d;

    do {
        saved_a = a;
        saved_b = b;
        saved_c = c;
        saved_d = d;

        /* Round 1 */
        STEP(F, a, b, c, d, SET(0), 0xd76aa478, 7)
        STEP(F, d, a, b, c, SET(1), 0xe8c7b756, 12)
        STEP(F, c, d, a, b, SET(2), 0x242070db, 17)
        STEP(F, b, c, d, a, SET(3), 0xc1bdceee, 22)
        STEP(F, a, b, c, d, SET(4), 0xf57c0faf, 7)
        STEP(F, d, a, b, c, SET(5), 0x4787c62a, 12)
        STEP(F, c, d, a, b, SET(6), 0xa8304613, 17)
        STEP(F, b, c, d, a, SET(7), 0xfd469501, 22)
        STEP(F, a, b, c, d, SET(8), 0x698098d8, 7)
        STEP(F, d, a, b, c, SET(9), 0x8b44f7af, 12)
        STEP(F, c, d, a, b, SET(10), 0xffff5bb1, 17)
        STEP(F, b, c, d, a, SET(11), 0x895cd7be, 22)
        STEP(F, a, b, c, d, SET(12), 0x6b901122, 7)
        STEP(F, d, a, b, c, SET(13), 0xfd987193, 12)
        STEP(F, c, d, a, b, SET(14), 0xa679438e, 17)
        STEP(F, b, c, d, a, SET(15), 0x49b40821, 22)

        /* Round 2 */
        STEP(G, a, b, c, d, GET(1), 0xf61e2562, 5)
        STEP(G, d, a, b, c, GET(6), 0xc040b340, 9)
        STEP(G, c, d, a, b, GET(11), 0x265e5a51, 14)
        STEP(G, b, c, d, a, GET(0), 0xe9b6c7aa, 20)
        STEP(G, a, b, c, d, GET(5), 0xd62f105d, 5)
        STEP(G, d, a, b, c, GET(10), 0x02441453, 9)
        STEP(G, c, d, a, b, GET(15), 0xd8a1e681, 14)
        STEP(G, b, c, d, a, GET(4), 0xe7d3fbc8, 20)
        STEP(G, a, b, c, d, GET(9), 0x21e1cde6, 5)
        STEP(G, d, a, b, c, GET(14), 0xc33707d6, 9)
        STEP(G, c, d, a, b, GET(3), 0xf4d50d87, 14)
        STEP(G, b, c, d, a, GET(8), 0x455a14ed, 20)
        STEP(G, a, b, c, d, GET(13), 0xa9e3e905, 5)
        STEP(G, d, a, b, c, GET(2), 0xfcefa3f8, 9)
        STEP(G, c, d, a, b, GET(7), 0x676f02d9, 14)
        STEP(G, b, c, d, a, GET(12), 0x8d2a4c8a, 20)

        /* Round 3 */
        STEP(H, a, b, c, d, GET(5), 0xfffa3942, 4)
        STEP(H2, d, a, b, c, GET(8), 0x8771f681, 11)
        STEP(H, c, d, a, b, GET(11), 0x6d9d6122, 16)
        STEP(H2, b, c, d, a, GET(14), 0xfde5380c, 23)
        STEP(H, a, b, c, d, GET(1), 0xa4beea44, 4)
        STEP(H2, d, a, b, c, GET(4), 0x4bdecfa9, 11)
        STEP(H, c, d, a, b, GET(7), 0xf6bb4b60, 16)
        STEP(H2, b, c, d, a, GET(10), 0xbebfbc70, 23)
        STEP(H, a, b, c, d, GET(13), 0x289b7ec6, 4)
        STEP(H2, d, a, b, c, GET(0), 0xeaa127fa, 11)
        STEP(H, c, d, a, b, GET(3), 0xd4ef3085, 16)
        STEP(H2, b, c, d, a, GET(6), 0x04881d05, 23)
        STEP(H, a, b, c, d, GET(9), 0xd9d4d039, 4)
        STEP(H2, d, a, b, c, GET(12), 0xe6db99e5, 11)
        STEP(H, c, d, a, b, GET(15), 0x1fa27cf8, 16)
        STEP(H2, b, c, d, a, GET(2), 0xc4ac5665, 23)

        /* Round 4 */
        STEP(I, a, b, c, d, GET(0), 0xf4292244, 6)
        STEP(I, d, a, b, c, GET(7), 0x432aff97, 10)
        STEP(I, c, d, a, b, GET(14), 0xab9423a7, 15)
        STEP(I, b, c, d, a, GET(5), 0xfc93a039, 21)
        STEP(I, a, b, c, d, GET(12), 0x655b59c3, 6)
        STEP(I, d, a, b, c, GET(3), 0x8f0ccc92, 10)
        STEP(I, c, d, a, b, GET(10), 0xffeff47d, 15)
        STEP(I, b, c, d, a, GET(1), 0x85845dd1, 21)
        STEP(I, a, b, c, d, GET(8), 0x6fa87e4f, 6)
        STEP(I, d, a, b, c, GET(15), 0xfe2ce6e0, 10)
        STEP(I, c, d, a, b, GET(6), 0xa3014314, 15)
        STEP(I, b, c, d, a, GET(13), 0x4e0811a1, 21)
        STEP(I, a, b, c, d, GET(4), 0xf7537e82, 6)
        STEP(I, d, a, b, c, GET(11), 0xbd3af235, 10)
        STEP(I, c, d, a, b, GET(2), 0x2ad7d2bb, 15)
        STEP(I, b, c, d, a, GET(9), 0xeb86d391, 21)

        a += saved_a;
        b += saved_b;
        c += saved_c;
        d += saved_d;

        ptr += 64;
    } while (size -= 64);

    ctx->a = a;
    ctx->b = b;
    ctx->c = c;
    ctx->d = d;

    return ptr;
}

static void MD5_Init(MD5_CTX *ctx)
{
    ctx->a = 0x67452301;
    ctx->b = 0xefcdab89;
    ctx->c = 0x98badcfe;
    ctx->d = 0x10325476;

    ctx->lo = 0;
    ctx->hi = 0;
}

static void MD5_Update(MD5_CTX *ctx, const void *data, unsigned long size)
{
    MD5_u32plus saved_lo;
    unsigned long used, available;

    saved_lo = ctx->lo;
    if ((ctx->lo = (saved_lo + size) & 0x1fffffff) < saved_lo)
        ctx->hi++;
    ctx->hi += size >> 29;

    used = saved_lo & 0x3f;

    if (used) {
        available = 64 - used;

        if (size < available) {
            memcpy(&ctx->buffer[used], data, size);
            return;
        }

        memcpy(&ctx->buffer[used], data, available);
        data = (const unsigned char *)data + available;
        size -= available;
        body(ctx, ctx->buffer, 64);
    }

    if (size >= 64) {
        data = body(ctx, data, size & ~(unsigned long)0x3f);
        size &= 0x3f;
    }

    memcpy(ctx->buffer, data, size);
}

#define MC_OUT(dst, src) \
    (dst)[0] = (unsigned char)(src); \
    (dst)[1] = (unsigned char)((src) >> 8); \
    (dst)[2] = (unsigned char)((src) >> 16); \
    (dst)[3] = (unsigned char)((src) >> 24);

static void MD5_Final(unsigned char *result, MD5_CTX *ctx)
{
    unsigned long used, available;

    used = ctx->lo & 0x3f;

    ctx->buffer[used++] = 0x80;

    available = 64 - used;

    if (available < 8) {
        memset(&ctx->buffer[used], 0, available);
        body(ctx, ctx->buffer, 64);
        used = 0;
        available = 64;
    }

    memset(&ctx->buffer[used], 0, available - 8);

    ctx->lo <<= 3;
    MC_OUT(&ctx->buffer[56], ctx->lo)
    MC_OUT(&ctx->buffer[60], ctx->hi)

    body(ctx, ctx->buffer, 64);

    MC_OUT(&result[0], ctx->a)
    MC_OUT(&result[4], ctx->b)
    MC_OUT(&result[8], ctx->c)
    MC_OUT(&result[12], ctx->d)

    memset(ctx, 0, sizeof(*ctx));
}
").

%---------------------------------------------------------------------------%

:- pragma no_determinism_warning(func(md5sum/1)).
:- pragma foreign_proc("C",
    md5sum(In::in) = (Digest::out),
    [will_not_call_mercury, promise_pure, thread_safe, may_not_duplicate],
"
    MD5_CTX         ctx;
    unsigned char   sum[16];
    const char      hex[16] = ""0123456789abcdef"";
    char            hexbuf[sizeof(sum) * 2 + 1];
    char            *p;
    size_t          i;

    MD5_Init(&ctx);
    MD5_Update(&ctx, (const unsigned char *) In, strlen(In));
    MD5_Final(sum, &ctx);

    /* Convert to hexadecimal string representation. */
    p = hexbuf;
    for (i = 0; i < sizeof(sum); i++) {
        *p++ = hex[(sum[i] & 0xf0) >> 4];
        *p++ = hex[(sum[i] & 0x0f)];
    }
    *p = '\\0';

    MR_make_aligned_string_copy(Digest, hexbuf);
").

    % Implementation for non-C backends left as an exercise for the reader.
    %
md5sum(_) = _ :-
    sorry($file, $pred).

%---------------------------------------------------------------------------%
:- end_module libs.md5.
%---------------------------------------------------------------------------%
