Make ctz and high_bit faster and const-time-ish

They get compiled as const-time on x86-64 with GCC but I don't think
this can be totally relied on. But it is anyway an improvement.

And, faster, because we compute it recursively

1 files changed, 0 insertions, 5 deletions

diff --git a/src/lib/math/bigint/bigint.cpp b/src/lib/math/bigint/bigint.cpp
index d8861fe65..75c87e5b6 100644
--- a/src/lib/math/bigint/bigint.cpp
+++ b/src/lib/math/bigint/bigint.cpp
@@ -279,12 +279,7 @@ size_t BigInt::top_bits_free() const
    const size_t words = sig_words();
 
    const word top_word = word_at(words - 1);
-
-   // Need to unpoison due to high_bit not being const time
-   CT::unpoison(top_word);
-
    const size_t bits_used = high_bit(top_word);
-
    return BOTAN_MP_WORD_BITS - bits_used;
    }