#include "os.h"#include <libsec.h> /* rfc2104 */DigestState*hmac_x(uchar *p, ulong len, uchar *key, ulong klen, uchar *digest, DigestState *s,	DigestState*(*x)(uchar*, ulong, uchar*, DigestState*), int xlen){	int i;	uchar pad[Hmacblksz+1], innerdigest[256]; 	if(xlen > sizeof(innerdigest))		return nil;	if(klen > Hmacblksz){		if(xlen > Hmacblksz)			return nil;		(*x)(key, klen, innerdigest, nil);		key = innerdigest;		klen = xlen;	} 	/* first time through */	if(s == nil || s->seeded == 0){		memset(pad, 0x36, Hmacblksz);		pad[Hmacblksz] = 0;		for(i = 0; i < klen; i++)			pad[i] ^= key[i];		s = (*x)(pad, Hmacblksz, nil, s);		if(s == nil)			return nil;	} 	s = (*x)(p, len, nil, s);	if(digest == nil)		return s; 	/* last time through */	memset(pad, 0x5c, Hmacblksz);	pad[Hmacblksz] = 0;	for(i = 0; i < klen; i++)		pad[i] ^= key[i];	(*x)(nil, 0, innerdigest, s);	s = (*x)(pad, Hmacblksz, nil, nil);	(*x)(innerdigest, xlen, digest, s);	return nil;}