Simplify bn_mul_part_recursive.
The loop and the outermost special-cases are basically the same.
Change-Id: I5e3ca60ad9a04efa66b479eebf8c3637a11cdceb
Reviewed-on: https://boringssl-review.googlesource.com/25406
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/fipsmodule/bn/mul.c b/crypto/fipsmodule/bn/mul.c
index 0f905b1..352b7e5 100644
--- a/crypto/fipsmodule/bn/mul.c
+++ b/crypto/fipsmodule/bn/mul.c
@@ -465,48 +465,32 @@
bn_mul_recursive(&t[n2], t, &t[n], n, 0, 0, p);
bn_mul_recursive(r, a, b, n, 0, 0, p);
- int i = n / 2, j;
- if (tna > tnb) {
- j = tna - i;
+ OPENSSL_memset(&r[n2], 0, sizeof(BN_ULONG) * n2);
+ if (tna < BN_MUL_RECURSIVE_SIZE_NORMAL &&
+ tnb < BN_MUL_RECURSIVE_SIZE_NORMAL) {
+ bn_mul_normal(&r[n2], &a[n], tna, &b[n], tnb);
} else {
- j = tnb - i;
- }
-
- if (j == 0) {
- // If there is only a bottom half to the number, just do it. We know the
- // larger of |tna - i| and |tnb - i| is zero. The other is zero or -1
- // because |tna| and |tnb| differ by at most one.
- bn_mul_recursive(&r[n2], &a[n], &b[n], i, tna - i, tnb - i, p);
- // |bn_mul_recursive| only writes the bottom |i|*2 words.
- OPENSSL_memset(&r[n2 + i * 2], 0, sizeof(BN_ULONG) * (n2 - i * 2));
- } else if (j > 0) {
- // E.g,, n == 16, i == 8 and tna == 11.
- // |tna| and |tnb| are within one of each other, so if |tna| is larger and
- // tna > i, then we know tnb >= i, and this call is valid.
- bn_mul_part_recursive(&r[n2], &a[n], &b[n], i, tna - i, tnb - i, p);
- } else {
- // (j < 0) E.g., n == 16, i == 8 and tn == 5
- OPENSSL_memset(&r[n2], 0, sizeof(BN_ULONG) * n2);
- if (tna < BN_MUL_RECURSIVE_SIZE_NORMAL &&
- tnb < BN_MUL_RECURSIVE_SIZE_NORMAL) {
- bn_mul_normal(&r[n2], &a[n], tna, &b[n], tnb);
- } else {
- for (;;) {
- i /= 2;
- // These simplified conditions work exclusively because difference
- // between |tna| and |tnb| is 1 or 0.
- //
- // TODO(davidben): This loop condition is exactly the same as the
- // |j > 0| one but more complicated. Merge them.
- if (i < tna || i < tnb) {
- bn_mul_part_recursive(&r[n2], &a[n], &b[n], i, tna - i, tnb - i, p);
- break;
- }
- if (i == tna || i == tnb) {
- bn_mul_recursive(&r[n2], &a[n], &b[n], i, tna - i, tnb - i, p);
- break;
- }
+ int i = n;
+ for (;;) {
+ i /= 2;
+ if (i < tna || i < tnb) {
+ // E.g., n == 16, i == 8 and tna == 11. |tna| and |tnb| are within one
+ // of each other, so if |tna| is larger and tna > i, then we know
+ // tnb >= i, and this call is valid.
+ bn_mul_part_recursive(&r[n2], &a[n], &b[n], i, tna - i, tnb - i, p);
+ break;
}
+ if (i == tna || i == tnb) {
+ // If there is only a bottom half to the number, just do it. We know
+ // the larger of |tna - i| and |tnb - i| is zero. The other is zero or
+ // -1 by because of |tna| and |tnb| differ by at most one.
+ bn_mul_recursive(&r[n2], &a[n], &b[n], i, tna - i, tnb - i, p);
+ break;
+ }
+
+ // This loop will eventually terminate when |i| falls below
+ // |BN_MUL_RECURSIVE_SIZE_NORMAL| because we know one of |tna| and |tnb|
+ // exceeds that.
}
}
}
