From d7c19d68550eb6018e8581a73a351905f4cc435c Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 1 Jul 2015 18:07:48 -0400
Subject: [PATCH] Make sampler_random_fract() actually obey its API contract.
This function is documented to return a value in the range (0,1),
which is what its predecessor anl_random_fract() did. However, the
new version depends on pg_erand48() which returns a value in [0,1).
The possibility of returning zero creates hazards of division by zero
or trying to compute log(0) at some call sites, and it might well
break third-party modules using anl_random_fract() too. So let's
change it to never return zero. Spotted by Coverity.
Michael Paquier, cosmetically adjusted by me
---
src/backend/utils/misc/sampling.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/src/backend/utils/misc/sampling.c b/src/backend/utils/misc/sampling.c
index aaf1d6c4108..6191f797344 100644
--- a/src/backend/utils/misc/sampling.c
+++ b/src/backend/utils/misc/sampling.c
@@ -237,7 +237,14 @@ sampler_random_init_state(long seed, SamplerRandomState randstate)
double
sampler_random_fract(SamplerRandomState randstate)
{
- return pg_erand48(randstate);
+ double res;
+
+ /* pg_erand48 returns a value in [0.0 - 1.0), so we must reject 0 */
+ do
+ {
+ res = pg_erand48(randstate);
+ } while (res == 0.0);
+ return res;
}
--
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