Glynn Clements pisze:
Maciej Sieczka wrote:
$ r.mapcalc 'map=rand(-2147483648,2147483647)'
$ r.stats -1 map | sort -n | uniq
100%
-2147483647
-2147483646
Why only 2 values from 4294967295 possible? Region is big enough to
accomodate more than 2 values from the range:
res[i] = (lo == hi) ? lo : lo + x % (hi - lo);
The expression (hi - lo) is overflowing the range of a signed integer.
Also, x will be restricted to 0 <= x < 2^31, possibly less if the
system doesn't have lrand48().
The wrapping can be fixed by adding casts, i.e.:
res[i] = (lo == hi) ? lo : lo + (unsigned) x % (unsigned) (hi - lo);
The 31-bit limitation can be fixed by replacing lrand48() with
mrand48(), which covers the full (signed) 32-bit range.
The attached patch appears to work.
Will you apply it?
One final point: -2^31 (= 0x80000000 = -2147483648) is the null value
for the CELL type, so you'll never see that value in a map.
BTW, what are the NULL value for double and float?
Maciek
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