/*
 * WjCryptLib_Md5 (https://github.com/WaterJuice/WjCryptLib)
 * Implementation of MD5 hash function. Originally written by Alexander Peslyak.
 * Modified by WaterJuice retaining Public Domain license.
 * This is free and unencumbered software released into the public domain - June 2013 - waterjuice.org
 */

#include <stdint.h>
#include <stdio.h>
#include <memory.h>

#include "lib_md5.h"

/* INTERNAL FUNCTIONS */

/*  F, G, H, I
 *
 *  The basic MD5 functions.
 * F and G are optimised 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 I( x, y, z )    ((y) ^ ((x) | ~(z)))

/* STEP: 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);

/* TransformFunction
 * This processes one or more 64-byte data blocks, but does NOT update the bit counters.
 * There are no alignment requirements.
 */
static void* TransformFunction(Md5Context* ctx, void const* data, uintmax_t size) {
    uint8_t*     ptr;
    uint32_t a;
    uint32_t b;
    uint32_t c;
    uint32_t d;
    uint32_t saved_a;
    uint32_t saved_b;
    uint32_t saved_c;
    uint32_t saved_d;

    #define GET(n) (ctx->block[(n)])
    #define SET(n) (ctx->block[(n)] = ((uint32_t) ptr[(n) * 4 + 0] << 0) |  \
                                      ((uint32_t) ptr[(n) * 4 + 1] << 8) | \
                                      ((uint32_t) ptr[(n) * 4 + 2] << 16) | \
                                      ((uint32_t) ptr[(n) * 4 + 3] << 24))

    ptr = (uint8_t*)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( H, d, a, b, c, GET(8),  0x8771f681, 11 )
        STEP( H, c, d, a, b, GET(11), 0x6d9d6122, 16 )
        STEP( H, b, c, d, a, GET(14), 0xfde5380c, 23 )
        STEP( H, a, b, c, d, GET(1),  0xa4beea44, 4 )
        STEP( H, d, a, b, c, GET(4),  0x4bdecfa9, 11 )
        STEP( H, c, d, a, b, GET(7),  0xf6bb4b60, 16 )
        STEP( H, b, c, d, a, GET(10), 0xbebfbc70, 23 )
        STEP( H, a, b, c, d, GET(13), 0x289b7ec6, 4 )
        STEP( H, d, a, b, c, GET(0),  0xeaa127fa, 11 )
        STEP( H, c, d, a, b, GET(3),  0xd4ef3085, 16 )
        STEP( H, b, c, d, a, GET(6),  0x04881d05, 23 )
        STEP( H, a, b, c, d, GET(9),  0xd9d4d039, 4 )
        STEP( H, d, a, b, c, GET(12), 0xe6db99e5, 11 )
        STEP( H, c, d, a, b, GET(15), 0x1fa27cf8, 16 )
        STEP( H, 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;

    #undef GET
    #undef SET

    return (ptr);
}

/*  EXPORTED FUNCTIONS */

/* Md5Initialise
 * Initialises an MD5 Context.
 * Use this to initialise/reset a context.
 */
void Md5Initialise(Md5Context* Context /* [out] */) {
    Context->a = 0x67452301;
    Context->b = 0xefcdab89;
    Context->c = 0x98badcfe;
    Context->d = 0x10325476;

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

/* Md5Update
 * Adds data to the MD5 context.
 * This will process the data and update the internal state of the context.
 * Keep on calling this function until all the data has been added.
 * Then call Md5Finalise to calculate the hash.
 */
void Md5Update(Md5Context* Context /* [in out] */, void const* Buffer /* [in] */, uint32_t BufferSize /* [in] */) {
    uint32_t saved_lo;
    uint32_t used;
    uint32_t free;

    saved_lo = Context->lo;

    if((Context->lo = (saved_lo + BufferSize) & 0x1fffffff) < saved_lo) {
        Context->hi++;
    }

    Context->hi += (uint32_t) (BufferSize >> 29);

    used = saved_lo & 0x3f;

    if( used ) {
        free = 64 - used;

        if( BufferSize < free ) {
            memcpy( &Context->buffer[used], Buffer, BufferSize );
            return;
        }

        memcpy( &Context->buffer[used], Buffer, free );
        Buffer = (uint8_t*)Buffer + free;
        BufferSize -= free;
        TransformFunction(Context, Context->buffer, 64);
    }

    if( BufferSize >= 64 ) {
        Buffer = TransformFunction( Context, Buffer, BufferSize & ~(uint32_t) 0x3f );
        BufferSize &= 0x3f;
    }

    memcpy( Context->buffer, Buffer, BufferSize );
}

/* Md5Finalise
 * Performs the final calculation of the hash and returns the digest
 * (16 byte buffer containing 128bit hash).
 * After calling this, Md5Initialised must be used to reuse the context.
 */
void Md5Finalise(Md5Context* Context /* [in out] */, MD5_HASH* Digest /* [in] */) {
    uint32_t used;
    uint32_t free;

    used = Context->lo & 0x3f;

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

    free = 64 - used;

    if(free < 8) {
        memset( &Context->buffer[used], 0, free );
        TransformFunction( Context, Context->buffer, 64 );
        used = 0;
        free = 64;
    }

    memset( &Context->buffer[used], 0, free - 8 );

    Context->lo <<= 3;
    Context->buffer[56] = (uint8_t) (Context->lo);
    Context->buffer[57] = (uint8_t) (Context->lo >> 8);
    Context->buffer[58] = (uint8_t) (Context->lo >> 16);
    Context->buffer[59] = (uint8_t) (Context->lo >> 24);
    Context->buffer[60] = (uint8_t) (Context->hi);
    Context->buffer[61] = (uint8_t) (Context->hi >> 8);
    Context->buffer[62] = (uint8_t) (Context->hi >> 16);
    Context->buffer[63] = (uint8_t) (Context->hi >> 24);

    TransformFunction( Context, Context->buffer, 64 );

    Digest->bytes[0]  = (uint8_t) (Context->a);
    Digest->bytes[1]  = (uint8_t) (Context->a >> 8);
    Digest->bytes[2]  = (uint8_t) (Context->a >> 16);
    Digest->bytes[3]  = (uint8_t) (Context->a >> 24);
    Digest->bytes[4]  = (uint8_t) (Context->b);
    Digest->bytes[5]  = (uint8_t) (Context->b >> 8);
    Digest->bytes[6]  = (uint8_t) (Context->b >> 16);
    Digest->bytes[7]  = (uint8_t) (Context->b >> 24);
    Digest->bytes[8]  = (uint8_t) (Context->c);
    Digest->bytes[9]  = (uint8_t) (Context->c >> 8);
    Digest->bytes[10] = (uint8_t) (Context->c >> 16);
    Digest->bytes[11] = (uint8_t) (Context->c >> 24);
    Digest->bytes[12] = (uint8_t) (Context->d);
    Digest->bytes[13] = (uint8_t) (Context->d >> 8);
    Digest->bytes[14] = (uint8_t) (Context->d >> 16);
    Digest->bytes[15] = (uint8_t) (Context->d >> 24);
}

/* Md5Calculate
 * Combines Md5Initialise, Md5Update, and Md5Finalise into one function.
 * Calculates the MD5 hash of the buffer.
 */
void Md5Calculate(void const* Buffer /* [in] */, uint32_t BufferSize /* [in] */, MD5_HASH* Digest /* [in] */) {
    Md5Context context;

    Md5Initialise( &context );
    Md5Update( &context, Buffer, BufferSize );
    Md5Finalise( &context, Digest );
}
