X-Git-Url: https://git.openssl.org/?p=openssl.git;a=blobdiff_plain;f=crypto%2Fbn%2Fbn_lib.c;h=60e3c680bc1813353614696b51cea4434c4dd56f;hp=0719514c720adf7d9e0113803ce494024a9cd103;hb=33d4e690ccd7cfc673af89d299e815ed35cc844a;hpb=320a14cb5b12cbdd2ff4d81c1e9a2ea7a139a038

diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c
index 0719514c72..60e3c680bc 100644
--- a/crypto/bn/bn_lib.c
+++ b/crypto/bn/bn_lib.c
@@ -56,11 +56,18 @@
  * [including the GNU Public Licence.]
  */
 
+#ifndef BN_DEBUG
+# undef NDEBUG /* avoid conflicting definitions */
+# define NDEBUG
+#endif
+
+#include <assert.h>
+#include <limits.h>
 #include <stdio.h>
 #include "cryptlib.h"
 #include "bn_lcl.h"
 
-char *BN_version="Big Number part of OpenSSL 0.9.1c 23-Dec-1998";
+const char *BN_version="Big Number" OPENSSL_VERSION_PTEXT;
 
 /* For a 32 bit machine
  * 2 -   4 ==  128
@@ -71,17 +78,16 @@ char *BN_version="Big Number part of OpenSSL 0.9.1c 23-Dec-1998";
  * 7 - 128 == 4096
  * 8 - 256 == 8192
  */
-int bn_limit_bits=0;
-int bn_limit_num=8;        /* (1<<bn_limit_bits) */
-int bn_limit_bits_low=0;
-int bn_limit_num_low=8;    /* (1<<bn_limit_bits_low) */
-int bn_limit_bits_high=0;
-int bn_limit_num_high=8;   /* (1<<bn_limit_bits_high) */
-int bn_limit_bits_mont=0;
-int bn_limit_num_mont=8;   /* (1<<bn_limit_bits_mont) */
-
-void BN_set_params(mult,high,low,mont)
-int mult,high,low,mont;
+static int bn_limit_bits=0;
+static int bn_limit_num=8;        /* (1<<bn_limit_bits) */
+static int bn_limit_bits_low=0;
+static int bn_limit_num_low=8;    /* (1<<bn_limit_bits_low) */
+static int bn_limit_bits_high=0;
+static int bn_limit_num_high=8;   /* (1<<bn_limit_bits_high) */
+static int bn_limit_bits_mont=0;
+static int bn_limit_num_mont=8;   /* (1<<bn_limit_bits_mont) */
+
+void BN_set_params(int mult, int high, int low, int mont)
 	{
 	if (mult >= 0)
 		{
@@ -113,8 +119,7 @@ int mult,high,low,mont;
 		}
 	}
 
-int BN_get_params(which)
-int which;
+int BN_get_params(int which)
 	{
 	if      (which == 0) return(bn_limit_bits);
 	else if (which == 1) return(bn_limit_bits_high);
@@ -123,7 +128,7 @@ int which;
 	else return(0);
 	}
 
-BIGNUM *BN_value_one()
+const BIGNUM *BN_value_one(void)
 	{
 	static BN_ULONG data_one=1L;
 	static BIGNUM const_one={&data_one,1,1,0};
@@ -131,7 +136,7 @@ BIGNUM *BN_value_one()
 	return(&const_one);
 	}
 
-char *BN_options()
+char *BN_options(void)
 	{
 	static int init=0;
 	static char data[16];
@@ -150,10 +155,9 @@ char *BN_options()
 	return(data);
 	}
 
-int BN_num_bits_word(l)
-BN_ULONG l;
+int BN_num_bits_word(BN_ULONG l)
 	{
-	static char bits[256]={
+	static const char bits[256]={
 		0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,
 		5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
 		6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
@@ -238,8 +242,7 @@ BN_ULONG l;
 		}
 	}
 
-int BN_num_bits(a)
-BIGNUM *a;
+int BN_num_bits(const BIGNUM *a)
 	{
 	BN_ULONG l;
 	int i;
@@ -248,57 +251,48 @@ BIGNUM *a;
 
 	if (a->top == 0) return(0);
 	l=a->d[a->top-1];
+	assert(l != 0);
 	i=(a->top-1)*BN_BITS2;
-	if (l == 0)
-		{
-#if !defined(NO_STDIO) && !defined(WIN16)
-		fprintf(stderr,"BAD TOP VALUE\n");
-#endif
-		abort();
-		}
 	return(i+BN_num_bits_word(l));
 	}
 
-void BN_clear_free(a)
-BIGNUM *a;
+void BN_clear_free(BIGNUM *a)
 	{
 	int i;
 
 	if (a == NULL) return;
 	if (a->d != NULL)
 		{
-		memset(a->d,0,a->max*sizeof(a->d[0]));
+		memset(a->d,0,a->dmax*sizeof(a->d[0]));
 		if (!(BN_get_flags(a,BN_FLG_STATIC_DATA)))
-			Free(a->d);
+			OPENSSL_free(a->d);
 		}
 	i=BN_get_flags(a,BN_FLG_MALLOCED);
 	memset(a,0,sizeof(BIGNUM));
 	if (i)
-		Free(a);
+		OPENSSL_free(a);
 	}
 
-void BN_free(a)
-BIGNUM *a;
+void BN_free(BIGNUM *a)
 	{
 	if (a == NULL) return;
 	if ((a->d != NULL) && !(BN_get_flags(a,BN_FLG_STATIC_DATA)))
-		Free(a->d);
+		OPENSSL_free(a->d);
 	a->flags|=BN_FLG_FREE; /* REMOVE? */
 	if (a->flags & BN_FLG_MALLOCED)
-		Free(a);
+		OPENSSL_free(a);
 	}
 
-void BN_init(a)
-BIGNUM *a;
+void BN_init(BIGNUM *a)
 	{
 	memset(a,0,sizeof(BIGNUM));
 	}
 
-BIGNUM *BN_new()
+BIGNUM *BN_new(void)
 	{
 	BIGNUM *ret;
 
-	if ((ret=(BIGNUM *)Malloc(sizeof(BIGNUM))) == NULL)
+	if ((ret=(BIGNUM *)OPENSSL_malloc(sizeof(BIGNUM))) == NULL)
 		{
 		BNerr(BN_F_BN_NEW,ERR_R_MALLOC_FAILURE);
 		return(NULL);
@@ -306,157 +300,193 @@ BIGNUM *BN_new()
 	ret->flags=BN_FLG_MALLOCED;
 	ret->top=0;
 	ret->neg=0;
-	ret->max=0;
+	ret->dmax=0;
 	ret->d=NULL;
 	return(ret);
 	}
 
-
-BN_CTX *BN_CTX_new()
+/* This is used both by bn_expand2() and bn_dup_expand() */
+/* The caller MUST check that words > b->dmax before calling this */
+static BN_ULONG *bn_expand_internal(const BIGNUM *b, int words)
 	{
-	BN_CTX *ret;
+	BN_ULONG *A,*a = NULL;
+	const BN_ULONG *B;
+	int i;
+
+	if (words > (INT_MAX/(4*BN_BITS2)))
+		{
+		BNerr(BN_F_BN_EXPAND_INTERNAL,BN_R_BIGNUM_TOO_LONG);
+		return NULL;
+		}
 
-	ret=(BN_CTX *)Malloc(sizeof(BN_CTX));
-	if (ret == NULL)
+	bn_check_top(b);	
+	if (BN_get_flags(b,BN_FLG_STATIC_DATA))
+		{
+		BNerr(BN_F_BN_EXPAND_INTERNAL,BN_R_EXPAND_ON_STATIC_BIGNUM_DATA);
+		return(NULL);
+		}
+	a=A=(BN_ULONG *)OPENSSL_malloc(sizeof(BN_ULONG)*(words+1));
+	if (A == NULL)
 		{
-		BNerr(BN_F_BN_CTX_NEW,ERR_R_MALLOC_FAILURE);
+		BNerr(BN_F_BN_EXPAND_INTERNAL,ERR_R_MALLOC_FAILURE);
 		return(NULL);
 		}
+#if 1
+	B=b->d;
+	/* Check if the previous number needs to be copied */
+	if (B != NULL)
+		{
+		for (i=b->top>>2; i>0; i--,A+=4,B+=4)
+			{
+			/*
+			 * The fact that the loop is unrolled
+			 * 4-wise is a tribute to Intel. It's
+			 * the one that doesn't have enough
+			 * registers to accomodate more data.
+			 * I'd unroll it 8-wise otherwise:-)
+			 *
+			 *		<appro@fy.chalmers.se>
+			 */
+			BN_ULONG a0,a1,a2,a3;
+			a0=B[0]; a1=B[1]; a2=B[2]; a3=B[3];
+			A[0]=a0; A[1]=a1; A[2]=a2; A[3]=a3;
+			}
+		switch (b->top&3)
+			{
+		case 3:	A[2]=B[2];
+		case 2:	A[1]=B[1];
+		case 1:	A[0]=B[0];
+		case 0: /* workaround for ultrix cc: without 'case 0', the optimizer does
+		         * the switch table by doing a=top&3; a--; goto jump_table[a];
+		         * which fails for top== 0 */
+			;
+			}
+		}
 
-	BN_CTX_init(ret);
-	ret->flags=BN_FLG_MALLOCED;
-	return(ret);
+#else
+	memset(A,0,sizeof(BN_ULONG)*(words+1));
+	memcpy(A,b->d,sizeof(b->d[0])*b->top);
+#endif
+		
+	return(a);
 	}
 
-void BN_CTX_init(ctx)
-BN_CTX *ctx;
-	{
-	memset(ctx,0,sizeof(BN_CTX));
-	ctx->tos=0;
-	ctx->flags=0;
-	}
+/* This is an internal function that can be used instead of bn_expand2()
+ * when there is a need to copy BIGNUMs instead of only expanding the
+ * data part, while still expanding them.
+ * Especially useful when needing to expand BIGNUMs that are declared
+ * 'const' and should therefore not be changed.
+ * The reason to use this instead of a BN_dup() followed by a bn_expand2()
+ * is memory allocation overhead.  A BN_dup() followed by a bn_expand2()
+ * will allocate new memory for the BIGNUM data twice, and free it once,
+ * while bn_dup_expand() makes sure allocation is made only once.
+ */
 
-void BN_CTX_free(c)
-BN_CTX *c;
+BIGNUM *bn_dup_expand(const BIGNUM *b, int words)
 	{
-	int i;
+	BIGNUM *r = NULL;
+
+	/* This function does not work if
+	 *      words <= b->dmax && top < words
+	 * because BN_dup() does not preserve 'dmax'!
+	 * (But bn_dup_expand() is not used anywhere yet.)
+	 */
+	
+	if (words > b->dmax)
+		{
+		BN_ULONG *a = bn_expand_internal(b, words);
 
-	for (i=0; i<BN_CTX_NUM; i++)
-		BN_clear_free(&(c->bn[i]));
-	if (c->flags & BN_FLG_MALLOCED)
-		Free(c);
+		if (a)
+			{
+			r = BN_new();
+			if (r)
+				{
+				r->top = b->top;
+				r->dmax = words;
+				r->neg = b->neg;
+				r->d = a;
+				}
+			else
+				{
+				/* r == NULL, BN_new failure */
+				OPENSSL_free(a);
+				}
+			}
+		/* If a == NULL, there was an error in allocation in
+		   bn_expand_internal(), and NULL should be returned */
+		}
+	else
+		{
+		r = BN_dup(b);
+		}
+
+	return r;
 	}
 
-BIGNUM *bn_expand2(b, words)
-BIGNUM *b;
-int words;
-	{
-	BN_ULONG *A,*B,*a;
-	int i,j;
+/* This is an internal function that should not be used in applications.
+ * It ensures that 'b' has enough room for a 'words' word number
+ * and initialises any unused part of b->d with leading zeros.
+ * It is mostly used by the various BIGNUM routines. If there is an error,
+ * NULL is returned. If not, 'b' is returned. */
 
-	bn_check_top(b);
+BIGNUM *bn_expand2(BIGNUM *b, int words)
+	{
+	BN_ULONG *A;
+	int i;
 
-	if (words > b->max)
+	if (words > b->dmax)
 		{
-		bn_check_top(b);	
-		if (BN_get_flags(b,BN_FLG_STATIC_DATA))
+		BN_ULONG *a = bn_expand_internal(b, words);
+
+		if (a)
 			{
-			BNerr(BN_F_BN_EXPAND2,BN_R_EXPAND_ON_STATIC_BIGNUM_DATA);
-			return(NULL);
+			if (b->d)
+				OPENSSL_free(b->d);
+			b->d=a;
+			b->dmax=words;
 			}
-		a=A=(BN_ULONG *)Malloc(sizeof(BN_ULONG)*(words+1));
-		if (A == NULL)
+		else
+			b = NULL;
+		}
+	
+	/* NB: bn_wexpand() calls this only if the BIGNUM really has to grow */
+	if ((b != NULL) && (b->top < b->dmax))
+		{
+		A = &(b->d[b->top]);
+		for (i=(words - b->top)>>3; i>0; i--,A+=8)
 			{
-			BNerr(BN_F_BN_EXPAND2,ERR_R_MALLOC_FAILURE);
-			return(NULL);
+			A[0]=0; A[1]=0; A[2]=0; A[3]=0;
+			A[4]=0; A[5]=0; A[6]=0; A[7]=0;
 			}
-memset(A,0x5c,sizeof(BN_ULONG)*(words+1));
-#if 1
-		B=b->d;
-		if (B != NULL)
-			{
-			for (i=b->top&(~7); i>0; i-=8)
-				{
-				A[0]=B[0]; A[1]=B[1]; A[2]=B[2]; A[3]=B[3];
-				A[4]=B[4]; A[5]=B[5]; A[6]=B[6]; A[7]=B[7];
-				A+=8;
-				B+=8;
-				}
-			switch (b->top&7)
-				{
-			case 7:
-				A[6]=B[6];
-			case 6:
-				A[5]=B[5];
-			case 5:
-				A[4]=B[4];
-			case 4:
-				A[3]=B[3];
-			case 3:
-				A[2]=B[2];
-			case 2:
-				A[1]=B[1];
-			case 1:
-				A[0]=B[0];
-			case 0:
-				/* I need the 'case 0' entry for utrix cc.
-				 * If the optimiser is turned on, it does the
-				 * switch table by doing
-				 * a=top&7
-				 * a--;
-				 * goto jump_table[a];
-				 * If top is 0, this makes us jump to 0xffffffc 
-				 * which is rather bad :-(.
-				 * eric 23-Apr-1998
-				 */
-				;
-				}
-			B= &(b->d[b->top]);
-			j=b->max-8;
-			for (i=b->top; i<j; i+=8)
-				{
-				B[0]=0; B[1]=0; B[2]=0; B[3]=0;
-				B[4]=0; B[5]=0; B[6]=0; B[7]=0;
-				B+=8;
-				}
-			for (j+=8; i<j; i++)
-				{
-				B[0]=0;
-				B++;
-				}
-#else
-			memcpy(a->d,b->d,sizeof(b->d[0])*b->top);
-#endif
-		
-/*		memset(&(p[b->max]),0,((words+1)-b->max)*sizeof(BN_ULONG)); */
-/*	{ int i; for (i=b->max; i<words+1; i++) p[i]=i;} */
-			Free(b->d);
-			}
-
-		b->d=a;
-		b->max=words;
+		for (i=(words - b->top)&7; i>0; i--,A++)
+			A[0]=0;
 		}
-	return(b);
+		
+	return b;
 	}
 
-BIGNUM *BN_dup(a)
-BIGNUM *a;
+BIGNUM *BN_dup(const BIGNUM *a)
 	{
-	BIGNUM *r;
+	BIGNUM *r, *t;
+
+	if (a == NULL) return NULL;
 
 	bn_check_top(a);
 
-	r=BN_new();
-	if (r == NULL) return(NULL);
-	return((BIGNUM *)BN_copy(r,a));
+	t = BN_new();
+	if (t == NULL) return(NULL);
+	r = BN_copy(t, a);
+	/* now  r == t || r == NULL */
+	if (r == NULL)
+		BN_free(t);
+	return r;
 	}
 
-BIGNUM *BN_copy(a, b)
-BIGNUM *a;
-BIGNUM *b;
+BIGNUM *BN_copy(BIGNUM *a, const BIGNUM *b)
 	{
 	int i;
-	BN_ULONG *A,*B;
+	BN_ULONG *A;
+	const BN_ULONG *B;
 
 	bn_check_top(b);
 
@@ -466,47 +496,18 @@ BIGNUM *b;
 #if 1
 	A=a->d;
 	B=b->d;
-	for (i=b->top&(~7); i>0; i-=8)
-		{
-		A[0]=B[0];
-		A[1]=B[1];
-		A[2]=B[2];
-		A[3]=B[3];
-		A[4]=B[4];
-		A[5]=B[5];
-		A[6]=B[6];
-		A[7]=B[7];
-		A+=8;
-		B+=8;
-		}
-	switch (b->top&7)
-		{
-	case 7:
-		A[6]=B[6];
-	case 6:
-		A[5]=B[5];
-	case 5:
-		A[4]=B[4];
-	case 4:
-		A[3]=B[3];
-	case 3:
-		A[2]=B[2];
-	case 2:
-		A[1]=B[1];
-	case 1:
-		A[0]=B[0];
-        case 0:
-		/* I need the 'case 0' entry for utrix cc.
-		 * If the optimiser is turned on, it does the
-		 * switch table by doing
-		 * a=top&7
-		 * a--;
-		 * goto jump_table[a];
-		 * If top is 0, this makes us jump to 0xffffffc which is
-		 * rather bad :-(.
-		 * eric 23-Apr-1998
-		 */
-		;
+	for (i=b->top>>2; i>0; i--,A+=4,B+=4)
+		{
+		BN_ULONG a0,a1,a2,a3;
+		a0=B[0]; a1=B[1]; a2=B[2]; a3=B[3];
+		A[0]=a0; A[1]=a1; A[2]=a2; A[3]=a3;
+		}
+	switch (b->top&3)
+		{
+		case 3: A[2]=B[2];
+		case 2: A[1]=B[1];
+		case 1: A[0]=B[0];
+		case 0: ; /* ultrix cc workaround, see comments in bn_expand_internal */
 		}
 #else
 	memcpy(a->d,b->d,sizeof(b->d[0])*b->top);
@@ -520,17 +521,44 @@ BIGNUM *b;
 	return(a);
 	}
 
-void BN_clear(a)
-BIGNUM *a;
+void BN_swap(BIGNUM *a, BIGNUM *b)
+	{
+	int flags_old_a, flags_old_b;
+	BN_ULONG *tmp_d;
+	int tmp_top, tmp_dmax, tmp_neg;
+	
+	flags_old_a = a->flags;
+	flags_old_b = b->flags;
+
+	tmp_d = a->d;
+	tmp_top = a->top;
+	tmp_dmax = a->dmax;
+	tmp_neg = a->neg;
+	
+	a->d = b->d;
+	a->top = b->top;
+	a->dmax = b->dmax;
+	a->neg = b->neg;
+	
+	b->d = tmp_d;
+	b->top = tmp_top;
+	b->dmax = tmp_dmax;
+	b->neg = tmp_neg;
+	
+	a->flags = (flags_old_a & BN_FLG_MALLOCED) | (flags_old_b & BN_FLG_STATIC_DATA);
+	b->flags = (flags_old_b & BN_FLG_MALLOCED) | (flags_old_a & BN_FLG_STATIC_DATA);
+	}
+
+
+void BN_clear(BIGNUM *a)
 	{
 	if (a->d != NULL)
-		memset(a->d,0,a->max*sizeof(a->d[0]));
+		memset(a->d,0,a->dmax*sizeof(a->d[0]));
 	a->top=0;
 	a->neg=0;
 	}
 
-BN_ULONG BN_get_word(a)
-BIGNUM *a;
+BN_ULONG BN_get_word(const BIGNUM *a)
 	{
 	int i,n;
 	BN_ULONG ret=0;
@@ -543,15 +571,15 @@ BIGNUM *a;
 #ifndef SIXTY_FOUR_BIT /* the data item > unsigned long */
 		ret<<=BN_BITS4; /* stops the compiler complaining */
 		ret<<=BN_BITS4;
+#else
+		ret=0;
 #endif
 		ret|=a->d[i];
 		}
 	return(ret);
 	}
 
-int BN_set_word(a,w)
-BIGNUM *a;
-BN_ULONG w;
+int BN_set_word(BIGNUM *a, BN_ULONG w)
 	{
 	int i,n;
 	if (bn_expand(a,sizeof(BN_ULONG)*8) == NULL) return(0);
@@ -569,6 +597,8 @@ BN_ULONG w;
 #ifndef SIXTY_FOUR_BIT /* the data item > unsigned long */
 		w>>=BN_BITS4;
 		w>>=BN_BITS4;
+#else
+		w=0;
 #endif
 		a->d[i]=(BN_ULONG)w&BN_MASK2;
 		if (a->d[i] != 0) a->top=i+1;
@@ -576,11 +606,7 @@ BN_ULONG w;
 	return(1);
 	}
 
-/* ignore negative */
-BIGNUM *BN_bin2bn(s, len, ret)
-unsigned char *s;
-int len;
-BIGNUM *ret;
+BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret)
 	{
 	unsigned int i,m;
 	unsigned int n;
@@ -600,6 +626,7 @@ BIGNUM *ret;
 	i=((n-1)/BN_BYTES)+1;
 	m=((n-1)%(BN_BYTES));
 	ret->top=i;
+	ret->neg=0;
 	while (n-- > 0)
 		{
 		l=(l<<8L)| *(s++);
@@ -617,9 +644,7 @@ BIGNUM *ret;
 	}
 
 /* ignore negative */
-int BN_bn2bin(a, to)
-BIGNUM *a;
-unsigned char *to;
+int BN_bn2bin(const BIGNUM *a, unsigned char *to)
 	{
 	int n,i;
 	BN_ULONG l;
@@ -633,9 +658,7 @@ unsigned char *to;
 	return(n);
 	}
 
-int BN_ucmp(a, b)
-BIGNUM *a;
-BIGNUM *b;
+int BN_ucmp(const BIGNUM *a, const BIGNUM *b)
 	{
 	int i;
 	BN_ULONG t1,t2,*ap,*bp;
@@ -657,9 +680,7 @@ BIGNUM *b;
 	return(0);
 	}
 
-int BN_cmp(a, b)
-BIGNUM *a;
-BIGNUM *b;
+int BN_cmp(const BIGNUM *a, const BIGNUM *b)
 	{
 	int i;
 	int gt,lt;
@@ -700,9 +721,7 @@ BIGNUM *b;
 	return(0);
 	}
 
-int BN_set_bit(a, n)
-BIGNUM *a;
-int n;
+int BN_set_bit(BIGNUM *a, int n)
 	{
 	int i,j,k;
 
@@ -716,13 +735,11 @@ int n;
 		a->top=i+1;
 		}
 
-	a->d[i]|=(1L<<j);
+	a->d[i]|=(((BN_ULONG)1)<<j);
 	return(1);
 	}
 
-int BN_clear_bit(a, n)
-BIGNUM *a;
-int n;
+int BN_clear_bit(BIGNUM *a, int n)
 	{
 	int i,j;
 
@@ -730,14 +747,12 @@ int n;
 	j=n%BN_BITS2;
 	if (a->top <= i) return(0);
 
-	a->d[i]&=(~(1L<<j));
+	a->d[i]&=(~(((BN_ULONG)1)<<j));
 	bn_fix_top(a);
 	return(1);
 	}
 
-int BN_is_bit_set(a, n)
-BIGNUM *a;
-int n;
+int BN_is_bit_set(const BIGNUM *a, int n)
 	{
 	int i,j;
 
@@ -748,9 +763,7 @@ int n;
 	return((a->d[i]&(((BN_ULONG)1)<<j))?1:0);
 	}
 
-int BN_mask_bits(a,n)
-BIGNUM *a;
-int n;
+int BN_mask_bits(BIGNUM *a, int n)
 	{
 	int b,w;
 
@@ -768,9 +781,7 @@ int n;
 	return(1);
 	}
 
-int bn_cmp_words(a,b,n)
-BN_ULONG *a,*b;
-int n;
+int bn_cmp_words(const BN_ULONG *a, const BN_ULONG *b, int n)
 	{
 	int i;
 	BN_ULONG aa,bb;
@@ -787,3 +798,34 @@ int n;
 	return(0);
 	}
 
+/* Here follows a specialised variants of bn_cmp_words().  It has the
+   property of performing the operation on arrays of different sizes.
+   The sizes of those arrays is expressed through cl, which is the
+   common length ( basicall, min(len(a),len(b)) ), and dl, which is the
+   delta between the two lengths, calculated as len(a)-len(b).
+   All lengths are the number of BN_ULONGs...  */
+
+int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b,
+	int cl, int dl)
+	{
+	int n,i;
+	n = cl-1;
+
+	if (dl < 0)
+		{
+		for (i=dl; i<0; i++)
+			{
+			if (b[n-i] != 0)
+				return -1; /* a < b */
+			}
+		}
+	if (dl > 0)
+		{
+		for (i=dl; i>0; i--)
+			{
+			if (a[n+i] != 0)
+				return 1; /* a > b */
+			}
+		}
+	return bn_cmp_words(a,b,cl);
+	}