[erlang-questions] On OTP rand module difference between OTP 19 and OTP 20
Richard A. O'Keefe
Mon Sep 4 03:42:19 CEST 2017
On 2/09/17 12:53 AM, Raimo Niskanen wrote:
>> P = random(),
>> P =< 0.3 -> ...;
>> P =< 0.7 -> ...;
>> P > 0.7 -> ...
> Especially since decimal numbers below 1.0 have no exact representation as
> IEEE floating point numbers.
There is in fact an IEEE standard for *decimal* floating point numbers.
If memory serves me correctly, z/Series and POWER support it. There is
a supplement to the C standard for it. Software emulation is available.
See decimal32, decimal64, decimal128 in
or the actual IEEE 754-2008 if you have a copy (which I sadly don't).
In any case,
P = 10*rand(),
if P < 3 -> ...
; P < 7 -> ...
; P >= 7 -> ...
evades that issue. (With the numbers from drand48() the multiplication
is exact; with 53-bit random numbers it is not.)
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