diff options
Diffstat (limited to 'mp.c')
| -rw-r--r-- | mp.c | 133 |
1 files changed, 133 insertions, 0 deletions
@@ -0,0 +1,133 @@ +#include "types.h"
+#include "bigdeal.h"
+#include <memory.h>
+
+static char rcsid[] = "$Header: /home/sater/bridge/bigdeal/RCS/mp.c,v 1.10 2000/08/16 15:06:05 sater Exp $";
+
+/*
+ * Multiple precision arithmetic
+ * Format is 12 byte number( 96 bits), with lowest byte most significant
+ * (socalled bigendian format)
+ */
+
+void
+mp96_zero(byte *b)
+/*
+ * Sets b to zero
+ */
+{
+
+ memset(b, 0, L);
+}
+
+void
+mp96_one(byte *b)
+/*
+ * Sets b to one
+ */
+{
+
+ memset(b, 0, L-1);
+ b[L-1] = 1;
+}
+
+void
+mp96_assign(byte *b, byte *b1)
+/*
+ * Assign b1 to b
+ */
+{
+
+ memcpy(b, b1, L);
+}
+
+int
+mp96_add(byte *b,byte *b1,byte *b2)
+/*
+ * Computes b=b1+b2
+ * returns carry bit signifying overflow
+ */
+{
+ int i;
+ unsigned int h,carry;
+
+ carry = 0;
+ for (i=L-1; i>=0; i--) {
+ h = b1[i]+b2[i]+carry;
+ carry = h>=256 ? 1 : 0;
+ b[i] = h; /* Truncates to 8 bits automatically */
+ }
+ return carry;
+}
+
+int
+mp96_sub(byte *b,byte *b1,byte *b2)
+/*
+ * Computes b=b1-b2
+ * returns borrow bit signifying overflow
+ */
+{
+ int i,h;
+ unsigned int borrow;
+
+ borrow = 0;
+ for (i=L-1; i>=0; i--) {
+ h = b1[i]-b2[i]-borrow;
+ borrow = h<0 ? 1 : 0;
+ b[i] = h;
+ }
+ return borrow;
+}
+
+int
+mp96_cmp(byte *b1, byte *b2)
+/*
+ * Compares b1 with b2
+ * returns >0 when b1>b2, <0 when b1<b2, 0 when b1==b2
+ */
+ {
+ int i;
+ int diff;
+
+ for (i=0; i<L; i++) {
+ diff = b1[i] - b2[i];
+ if (diff)
+ return diff;
+ }
+ return 0;
+}
+
+void
+mp96_mul(byte *b,byte *b1,byte *b2)
+/*
+ * Computes b=b1*b2
+ * overflow goes undetected
+ */
+{
+ int i,j;
+ unsigned int h,carry;
+ byte b1copy[L],b2copy[L],bpart[L];
+
+ /*
+ * Make copies of input in case one of the inputs is also output
+ */
+ mp96_assign(b1copy, b1);
+ mp96_assign(b2copy, b2);
+
+ /*
+ * Here if an input is also output the input gets overwritten
+ */
+ mp96_zero(b);
+
+ for (i=L-1; i>=0; i--) {
+ for (j=L-1; j>i; j--)
+ bpart[j] = 0;
+ carry=0;
+ for (j=i; j>=0; j--) {
+ h = b1copy[i]*b2copy[L-1+j-i]+carry;
+ carry = h/256;
+ bpart[j] = h;
+ }
+ (void) mp96_add(b,b,bpart);
+ }
+}
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