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The following test suggests that GHC is overrounding Float subnormals, when printing them out

Prelude> 2**(-149)
1.401298464324817e-45
Prelude> 2**(-149) :: Float
1.0e-45
Prelude> isDenormalized it
True
Prelude>
Prelude> 2**(-149) * 2**(100) * 2**(49) :: Float
1.0

By comparison

#include <stdio.h>
#include <stdlib.h>

int main (void)
{
 float clang_dec, clang_hex, libc_dec, libc_hex;

 clang_dec = 1.401298464324817e-45;
 clang_hex = 0x0.000002P-126;
 printf("clang (from decimal)   = %a\n",clang_dec);
 printf("clang (from decimal)   = %g\n",clang_dec);
 printf("clang (from hex)       = %a\n",clang_hex);
 printf("clang (from hex)       = %g\n",clang_hex);

 libc_dec = strtod("1.401298464324817e-45",NULL);
 libc_hex = strtod("0x0.000002P-126",NULL);
 printf("libc (from decimal) = %a\n",libc_dec);
 printf("libc (from decimal) = %g\n",libc_dec);
 printf("libc (from hex)     = %a\n",libc_hex);
 printf("libc (from hex)     = %g\n",libc_hex);
}

produces

clang (from decimal)   = 0x1p-149
clang (from decimal)   = 1.4013e-45
clang (from hex)       = 0x1p-149
clang (from hex)       = 1.4013e-45
libc (from decimal) = 0x1p-149
libc (from decimal) = 1.4013e-45
libc (from hex)     = 0x1p-149
libc (from hex)     = 1.4013e-45

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	simonmar
Operating system
Architecture