my_md5.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

typedef union uwb {
  unsigned w;
  unsigned char b[4];
} WBunion;

typedef unsigned Digest[4];

unsigned f0( unsigned abcd[] ){
  return ( abcd[1] & abcd[2]) | (~abcd[1] & abcd[3]);}

unsigned f1( unsigned abcd[] ){
  return ( abcd[3] & abcd[1]) | (~abcd[3] & abcd[2]);}

unsigned f2( unsigned abcd[] ){
  return  abcd[1] ^ abcd[2] ^ abcd[3];}

unsigned f3( unsigned abcd[] ){
  return abcd[2] ^ (abcd[1] |~ abcd[3]);}

typedef unsigned (*DgstFctn)(unsigned a[]);

unsigned *calcKs( unsigned *k)
{
  double s, pwr;
  int i;

  pwr = pow( 2, 32);
  for (i=0; i<64; i++) {
    s = fabs(sin(1+i));
    k[i] = (unsigned)( s * pwr );
  }
  return k;
}

unsigned rol( unsigned v, short amt )
{
  unsigned  msk1 = (1<<amt) -1;
  return ((v>>(32-amt)) & msk1) | ((v<<amt) & ~msk1);
}

unsigned *md5( const char *msg, int mlen)
{
  static Digest h0 = { 0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476 };
  static DgstFctn ff[] = { &f0, &f1, &f2, &f3 };
  static short M[] = { 1, 5, 3, 7 };
  static short O[] = { 0, 1, 5, 0 };
  static short rot0[] = { 7,12,17,22};
  static short rot1[] = { 5, 9,14,20};
  static short rot2[] = { 4,11,16,23};
  static short rot3[] = { 6,10,15,21};
  static short *rots[] = {rot0, rot1, rot2, rot3 };
  static unsigned kspace[64];
  static unsigned *k;

  static Digest h;
  Digest abcd;
  DgstFctn fctn;
  short m, o, g;
  unsigned f;
  short *rotn;
  union {
    unsigned w[16];
    char     b[64];
  }mm;
  int os = 0;
  int grp, grps, q, p;
  unsigned char *msg2;

  if (k==NULL) k= calcKs(kspace);

  for (q=0; q<4; q++)
    h[q] = h0[q];
  grps  = 1 + (mlen+8)/64;
  msg2 = malloc( 64*grps);
  memcpy( msg2, msg, mlen);
  msg2[mlen] = (unsigned char)0x80;
  q = mlen + 1;
  while (q < 64*grps)
    {
      msg2[q] = 0;
      q++;
    }
  WBunion u;
  u.w = 8*mlen;
  q -= 8;
  memcpy(msg2+q, &u.w, 4 );

  for (grp=0; grp<grps; grp++)
    {
      memcpy( mm.b, msg2+os, 64);
      for(q=0;q<4;q++) abcd[q] = h[q];
      for (p = 0; p<4; p++) {
	fctn = ff[p];
	rotn = rots[p];
	m = M[p]; o= O[p];
	for (q=0; q<16; q++) {
	  g = (m*q + o) % 16;
	  f = abcd[1] + rol( abcd[0]+ fctn(abcd) + k[q+16*p] + mm.w[g], rotn[q%4]);

	  abcd[0] = abcd[3];
	  abcd[3] = abcd[2];
	  abcd[2] = abcd[1];
	  abcd[1] = f;
	}
      }
      for (p=0; p<4; p++)
	h[p] += abcd[p];
      os += 64;
    }

  if( msg2 )
    free( msg2 );

  return h;
}

int	main(int ac, char **av)
{
  int j,k;
  unsigned *d;
  WBunion u;

  if (ac < 2)
    return printf("\n");
  d = md5(av[1], strlen(av[1]));
  for (j=0;j<4; j++){
    u.w = d[j];
    for (k=0;k<4;k++) printf("%x",u.b[k]);
  }
  printf("\n");
  return 0;
}