[GHC] #9564: Floating point subnormals overrounded on output

#9564: Floating point subnormals overrounded on output -------------------------------------+------------------------------------- Reporter: jrp | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 7.8.3 Keywords: | Operating System: MacOS X Architecture: x86_64 (amd64) | Type of failure: Incorrect Difficulty: Unknown | result at runtime Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- 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 #include 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 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9564 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler