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authorDenys Vlasenko2017-07-09 00:39:15 +0200
committerDenys Vlasenko2017-07-09 00:39:15 +0200
commit9de9c871bf44b931c7a1bb66d3134e2deb811f88 (patch)
tree68f7f95835b7e2c1c60825e2745d00f5aacfd92b /coreutils
parentd18b2000967cddd0b84091d90a914aec58025310 (diff)
downloadbusybox-9de9c871bf44b931c7a1bb66d3134e2deb811f88.zip
busybox-9de9c871bf44b931c7a1bb66d3134e2deb811f88.tar.gz
shuf: fix random line selection. Closes 9971
""" For example, given input file: foo bar baz after shuffling the input file, foo will never end up back on the first line. This came to light when I ran into a use-case where someone was selecting a random line from a file using shuf | head -n 1, and the results on busybox were showing a statistical anomaly (as in, the first line would never ever be picked) vs the same process running on environments that had gnu coreutils installed. On line https://git.busybox.net/busybox/tree/coreutils/shuf.c#n56 it uses r %= i, which will result in 0 <= r < i, while the algorithm specifies 0 <= r <= i. """ Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'coreutils')
-rw-r--r--coreutils/shuf.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/coreutils/shuf.c b/coreutils/shuf.c
index 9f61f2f..217f15c 100644
--- a/coreutils/shuf.c
+++ b/coreutils/shuf.c
@@ -53,7 +53,7 @@ static void shuffle_lines(char **lines, unsigned numlines)
/* RAND_MAX can be as small as 32767 */
if (i > RAND_MAX)
r ^= rand() << 15;
- r %= i;
+ r %= i + 1;
tmp = lines[i];
lines[i] = lines[r];
lines[r] = tmp;