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Add nowrap u64 multiplication function

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Follows #30920

Signed-off-by: José M. Guisado <guigom@riseup.net>
This commit is contained in:
José M. Guisado 2019-09-18 12:30:28 +02:00
parent 7225cfc586
commit f237529fff
3 changed files with 25 additions and 0 deletions
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14
src/lib/intmath/muldiv.c
View File

@ -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

2
src/lib/intmath/muldiv.h
View File

@ -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>

9
src/test/test_util.c
View File

@ -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:
;
}