#include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/cryptohash.h>
  
  /* F, G and H are basic MD4 functions: selection, majority, parity */
  #define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
  #define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
  #define H(x, y, z) ((x) ^ (y) ^ (z))
  
  /*
   * The generic round function.  The application is so specific that
   * we don't bother protecting all the arguments with parens, as is generally
   * good macro practice, in favor of extra legibility.
   * Rotation is separate from addition to prevent recomputation
   */
  #define ROUND(f, a, b, c, d, x, s)	\
  	(a += f(b, c, d) + x, a = (a << s) | (a >> (32 - s)))
  #define K1 0
  #define K2 013240474631UL
  #define K3 015666365641UL
  
  /*
   * Basic cut-down MD4 transform.  Returns only 32 bits of result.
   */
  __u32 half_md4_transform(__u32 buf[4], __u32 const in[8])
  {
  	__u32 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
  
  	/* Round 1 */
  	ROUND(F, a, b, c, d, in[0] + K1,  3);
  	ROUND(F, d, a, b, c, in[1] + K1,  7);
  	ROUND(F, c, d, a, b, in[2] + K1, 11);
  	ROUND(F, b, c, d, a, in[3] + K1, 19);
  	ROUND(F, a, b, c, d, in[4] + K1,  3);
  	ROUND(F, d, a, b, c, in[5] + K1,  7);
  	ROUND(F, c, d, a, b, in[6] + K1, 11);
  	ROUND(F, b, c, d, a, in[7] + K1, 19);
  
  	/* Round 2 */
  	ROUND(G, a, b, c, d, in[1] + K2,  3);
  	ROUND(G, d, a, b, c, in[3] + K2,  5);
  	ROUND(G, c, d, a, b, in[5] + K2,  9);
  	ROUND(G, b, c, d, a, in[7] + K2, 13);
  	ROUND(G, a, b, c, d, in[0] + K2,  3);
  	ROUND(G, d, a, b, c, in[2] + K2,  5);
  	ROUND(G, c, d, a, b, in[4] + K2,  9);
  	ROUND(G, b, c, d, a, in[6] + K2, 13);
  
  	/* Round 3 */
  	ROUND(H, a, b, c, d, in[3] + K3,  3);
  	ROUND(H, d, a, b, c, in[7] + K3,  9);
  	ROUND(H, c, d, a, b, in[2] + K3, 11);
  	ROUND(H, b, c, d, a, in[6] + K3, 15);
  	ROUND(H, a, b, c, d, in[1] + K3,  3);
  	ROUND(H, d, a, b, c, in[5] + K3,  9);
  	ROUND(H, c, d, a, b, in[0] + K3, 11);
  	ROUND(H, b, c, d, a, in[4] + K3, 15);
  
  	buf[0] += a;
  	buf[1] += b;
  	buf[2] += c;
  	buf[3] += d;
  
  	return buf[1]; /* "most hashed" word */
  }
  EXPORT_SYMBOL(half_md4_transform);