Openssl 1.1.0h

crypto/bn/bn_add.c

@@ -0,0 +1,209 @@
+/*
+ * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the OpenSSL license (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include "internal/cryptlib.h"
+#include "bn_lcl.h"
+
+/* r can == a or b */
+int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
+{
+    int a_neg = a->neg, ret;
+
+    bn_check_top(a);
+    bn_check_top(b);
+
+    /*-
+     *  a +  b      a+b
+     *  a + -b      a-b
+     * -a +  b      b-a
+     * -a + -b      -(a+b)
+     */
+    if (a_neg ^ b->neg) {
+        /* only one is negative */
+        if (a_neg) {
+            const BIGNUM *tmp;
+
+            tmp = a;
+            a = b;
+            b = tmp;
+        }
+
+        /* we are now a - b */
+
+        if (BN_ucmp(a, b) < 0) {
+            if (!BN_usub(r, b, a))
+                return 0;
+            r->neg = 1;
+        } else {
+            if (!BN_usub(r, a, b))
+                return 0;
+            r->neg = 0;
+        }
+        return 1;
+    }
+
+    ret = BN_uadd(r, a, b);
+    r->neg = a_neg;
+    bn_check_top(r);
+    return ret;
+}
+
+/* unsigned add of b to a */
+int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
+{
+    int max, min, dif;
+    const BN_ULONG *ap, *bp;
+    BN_ULONG *rp, carry, t1, t2;
+
+    bn_check_top(a);
+    bn_check_top(b);
+
+    if (a->top < b->top) {
+        const BIGNUM *tmp;
+
+        tmp = a;
+        a = b;
+        b = tmp;
+    }
+    max = a->top;
+    min = b->top;
+    dif = max - min;
+
+    if (bn_wexpand(r, max + 1) == NULL)
+        return 0;
+
+    r->top = max;
+
+    ap = a->d;
+    bp = b->d;
+    rp = r->d;
+
+    carry = bn_add_words(rp, ap, bp, min);
+    rp += min;
+    ap += min;
+
+    while (dif) {
+        dif--;
+        t1 = *(ap++);
+        t2 = (t1 + carry) & BN_MASK2;
+        *(rp++) = t2;
+        carry &= (t2 == 0);
+    }
+    *rp = carry;
+    r->top += carry;
+
+    r->neg = 0;
+    bn_check_top(r);
+    return 1;
+}
+
+/* unsigned subtraction of b from a, a must be larger than b. */
+int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
+{
+    int max, min, dif;
+    BN_ULONG t1, t2, borrow, *rp;
+    const BN_ULONG *ap, *bp;
+
+    bn_check_top(a);
+    bn_check_top(b);
+
+    max = a->top;
+    min = b->top;
+    dif = max - min;
+
+    if (dif < 0) {              /* hmm... should not be happening */
+        BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3);
+        return 0;
+    }
+
+    if (bn_wexpand(r, max) == NULL)
+        return 0;
+
+    ap = a->d;
+    bp = b->d;
+    rp = r->d;
+
+    borrow = bn_sub_words(rp, ap, bp, min);
+    ap += min;
+    rp += min;
+
+    while (dif) {
+        dif--;
+        t1 = *(ap++);
+        t2 = (t1 - borrow) & BN_MASK2;
+        *(rp++) = t2;
+        borrow &= (t1 == 0);
+    }
+
+    while (max && *--rp == 0)
+        max--;
+
+    r->top = max;
+    r->neg = 0;
+    bn_pollute(r);
+
+    return 1;
+}
+
+int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
+{
+    int max;
+    int add = 0, neg = 0;
+
+    bn_check_top(a);
+    bn_check_top(b);
+
+    /*-
+     *  a -  b      a-b
+     *  a - -b      a+b
+     * -a -  b      -(a+b)
+     * -a - -b      b-a
+     */
+    if (a->neg) {
+        if (b->neg) {
+            const BIGNUM *tmp;
+
+            tmp = a;
+            a = b;
+            b = tmp;
+        } else {
+            add = 1;
+            neg = 1;
+        }
+    } else {
+        if (b->neg) {
+            add = 1;
+            neg = 0;
+        }
+    }
+
+    if (add) {
+        if (!BN_uadd(r, a, b))
+            return 0;
+        r->neg = neg;
+        return 1;
+    }
+
+    /* We are actually doing a - b :-) */
+
+    max = (a->top > b->top) ? a->top : b->top;
+    if (bn_wexpand(r, max) == NULL)
+        return 0;
+    if (BN_ucmp(a, b) < 0) {
+        if (!BN_usub(r, b, a))
+            return 0;
+        r->neg = 1;
+    } else {
+        if (!BN_usub(r, a, b))
+            return 0;
+        r->neg = 0;
+    }
+    bn_check_top(r);
+    return 1;
+}