Add BN_count_low_zero_bits.
This allows a BIGNUM consumer to avoid messing around with bn->d and
bn->top/width.
Bug: 232
Change-Id: I134cf412fef24eb404ff66c84831b4591d921a17
Reviewed-on: https://boringssl-review.googlesource.com/25484
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/include/openssl/bn.h b/include/openssl/bn.h
index 495e338..871ba33 100644
--- a/include/openssl/bn.h
+++ b/include/openssl/bn.h
@@ -459,6 +459,7 @@
// BN_is_pow2 returns 1 if |a| is a power of two, and 0 otherwise.
OPENSSL_EXPORT int BN_is_pow2(const BIGNUM *a);
+
// Bitwise operations.
// BN_lshift sets |r| equal to |a| << n. The |a| and |r| arguments may be the
@@ -495,6 +496,11 @@
// on success or zero if |n| is greater than the length of |a| already.
OPENSSL_EXPORT int BN_mask_bits(BIGNUM *a, int n);
+// BN_count_low_zero_bits returns the number of low-order zero bits in |bn|, or
+// the number of factors of two which divide it. It returns zero if |bn| is
+// zero.
+OPENSSL_EXPORT int BN_count_low_zero_bits(const BIGNUM *bn);
+
// Modulo arithmetic.
