From f237529fff657bbbf8d2f2632337d9848446d7da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20M=2E=20Guisado?= <guigom@riseup.net>
Date: Wed, 18 Sep 2019 12:30:28 +0200
Subject: [PATCH] Add nowrap u64 multiplication function
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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 6a292db7ba..3330a4c569 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 64500b6dce..7aa0f9b235 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 84834f4d6c..90e1b080b1 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:
;
}
--
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