From: Søren Sandmann Pedersen <[email protected]>
The lcg_rand() function only returns 15 random bits, so lcg_rand_u32()
would always have 0 in bit 31 and bit 15. Fix that by calling
lcg_rand() three times, to generate 15, 15, and 2 random bits
respectively.
V2: Use the 10/11 most significant bits from the 3 lcg results and mix
them with the low ones from the adjacent one, as suggested by Andrea
Canciani.
---
test/utils.h | 12 ++++++++----
1 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/test/utils.h b/test/utils.h
index 615ad78..000aaa6 100644
--- a/test/utils.h
+++ b/test/utils.h
@@ -44,10 +44,14 @@ lcg_rand_N (int max)
static inline uint32_t
lcg_rand_u32 (void)
{
- uint32_t lo = lcg_rand();
- uint32_t hi = lcg_rand();
-
- return (hi << 16) | lo;
+ /* This uses the 10/11 most significant bits from the 3 lcg results
+ * (and mixes them with the low from the adjacent one).
+ */
+ uint32_t lo = lcg_rand() >> -(32 - 15 - 11 * 2);
+ uint32_t mid = lcg_rand() << (32 - 15 - 11 * 1);
+ uint32_t hi = lcg_rand() << (32 - 15 - 11 * 0);
+
+ return (hi ^ mid ^ lo);
}
/* CRC 32 computation
--
1.7.4
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