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http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=194842 

Because RAND_MAX is equal to INT_MAX, the following expression
contained in the manpage for rand(3) is slightly incorrect.
j=1+(int) (10.0*rand()/(RAND_MAX+1.0));

The correct expression should use parentheses to group the division
before the multiplication, thus yielding:
j=1+(int) (10.0*(rand()/(RAND_MAX+1.0)));

This is not an error where 10.0 is a floating point number, however
where 10.0 is replaced with an integer, this will cause the expression
to always evaluate to 1. (The addition of two parentheses would make
this bug a lot more difficult to make.)
This commit is contained in:
Michael Kerrisk 2005-06-21 09:22:02 +00:00
parent 3876c0e522
commit 6e657687f9
1 changed files with 2 additions and 2 deletions
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man3/rand.3
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@ -130,13 +130,13 @@ p. 277)), the following comments are made:
always do it by using high-order bits, as in
.RS
.sp
j=1+(int) (10.0*rand()/(RAND_MAX+1.0));
j = 1 + (int) (10.0 * (rand() / (RAND_MAX + 1.0)));
.sp
.RE
and never by anything resembling
.RS
.sp
j=1+(rand() % 10);
j = 1 + (rand() % 10);
.sp
.RE
(which uses lower-order bits)."