commit f237529fff657bbbf8d2f2632337d9848446d7da Author: José M. Guisado guigom@riseup.net Date: Wed Sep 18 12:30:28 2019 +0200

Add nowrap u64 multiplication function

Follows #30920

Signed-off-by: José M. Guisado guigom@riseup.net --- src/lib/intmath/muldiv.c | 14 ++++++++++++++ src/lib/intmath/muldiv.h | 2 ++ src/test/test_util.c | 9 +++++++++ 3 files changed, 25 insertions(+)

diff --git a/src/lib/intmath/muldiv.c b/src/lib/intmath/muldiv.c index 6a292db7b..3330a4c56 100644 --- a/src/lib/intmath/muldiv.c +++ b/src/lib/intmath/muldiv.c @@ -69,6 +69,20 @@ gcd64(uint64_t a, uint64_t b) return a; }

+/** Return the unsigned integer product of <b>a</b> and <b>b</b>, if overflow + * is detected return UINT64_MAX instead. */ +uint64_t +tor_mul_u64_nowrap(uint64_t a, uint64_t b) +{ + if (a == 0 || b == 0) { + return 0; + } else if (PREDICT_UNLIKELY(UINT64_MAX / a < b)) { + return UINT64_MAX; + } else { + return a*b; + } +} + /* Given a fraction *<b>numer</b> / *<b>denom</b>, simplify it. * Requires that the denominator is greater than 0. */ void diff --git a/src/lib/intmath/muldiv.h b/src/lib/intmath/muldiv.h index 64500b6dc..7aa0f9b23 100644 --- a/src/lib/intmath/muldiv.h +++ b/src/lib/intmath/muldiv.h @@ -18,6 +18,8 @@ unsigned round_to_next_multiple_of(unsigned number, unsigned divisor); uint32_t round_uint32_to_next_multiple_of(uint32_t number, uint32_t divisor); uint64_t round_uint64_to_next_multiple_of(uint64_t number, uint64_t divisor);

+uint64_t tor_mul_u64_nowrap(uint64_t a, uint64_t b); + void simplify_fraction64(uint64_t *numer, uint64_t *denom);

/* Compute the CEIL of <b>a</b> divided by <b>b</b>, for nonnegative <b>a</b> diff --git a/src/test/test_util.c b/src/test/test_util.c index 84834f4d6..90e1b080b 100644 --- a/src/test/test_util.c +++ b/src/test/test_util.c @@ -33,6 +33,7 @@ #include "lib/process/env.h" #include "lib/process/pidfile.h" #include "lib/intmath/weakrng.h" +#include "lib/intmath/muldiv.h" #include "lib/thread/numcpus.h" #include "lib/math/fp.h" #include "lib/math/laplace.h" @@ -5973,6 +5974,14 @@ test_util_nowrap_math(void *arg) tt_u64_op(UINT32_MAX, OP_EQ, tor_add_u32_nowrap(2, UINT32_MAX-1)); tt_u64_op(UINT32_MAX, OP_EQ, tor_add_u32_nowrap(UINT32_MAX, UINT32_MAX));

+ tt_u64_op(0, OP_EQ, tor_mul_u64_nowrap(0, 0)); + tt_u64_op(1, OP_EQ, tor_mul_u64_nowrap(1, 1)); + tt_u64_op(2, OP_EQ, tor_mul_u64_nowrap(2, 1)); + tt_u64_op(4, OP_EQ, tor_mul_u64_nowrap(2, 2)); + tt_u64_op(UINT64_MAX, OP_EQ, tor_mul_u64_nowrap(UINT64_MAX, 1)); + tt_u64_op(UINT64_MAX, OP_EQ, tor_mul_u64_nowrap(2, UINT64_MAX)); + tt_u64_op(UINT64_MAX, OP_EQ, tor_mul_u64_nowrap(UINT64_MAX, UINT64_MAX)); + done: ; }