[tor-commits] [tor/master] Use the | trick to save a comparison in our calloc check.

[nickm at torproject.org]

commit ded33cb2c73151e2f02a8a1d520b54e4f1c14072
Author: Nick Mathewson <nickm at torproject.org>
Date:   Sun Nov 2 11:48:08 2014 -0500

    Use the | trick to save a comparison in our calloc check.
---
 src/common/util.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/common/util.c b/src/common/util.c
index 006fd80..3d81f2b 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -206,8 +206,15 @@ tor_malloc_zero_(size_t size DMALLOC_PARAMS)
 static INLINE int
 size_mul_check(const size_t x, const size_t y)
 {
-  return ((x < SQRT_SIZE_MAX_P1 && y < SQRT_SIZE_MAX_P1) ||
-          y == 0 || x <= SIZE_MAX / y);
+  /* This first check is equivalent to
+     (x < SQRT_SIZE_MAX_P1 && y < SQRT_SIZE_MAX_P1)
+
+     Rationale: if either one of x or y is >= SQRT_SIZE_MAX_P1, then it
+     will have some bit set in its most significant half.
+   */
+  return ((x|y) < SQRT_SIZE_MAX_P1 ||
+          y == 0 ||
+          x <= SIZE_MAX / y);
 }
 
 /** Allocate a chunk of <b>nmemb</b>*<b>size</b> bytes of memory, fill