#8285: unexpected behavior with encodeFloat on large inputs -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- @@ -1,1 +1,3 @@ - benjamin scarlet discovered some unexpected behavior in encodeFloat today + {{{ + > encodeFloat 1 1023 + 8.98846567431158e307 -- ok @@ -3,3 +5,2 @@ - {{{ - <bscarlet> > map (\x -> encodeFloat 1 (shiftL 1 x)) [30,31] - [23:47:47] <lambdabot> [Infinity,0.0] + > encodeFloat 1 1024 + Infinity -- ok @@ -7,2 +8,2 @@ - [23:49:09] <arkeet> > encodeFloat 1 60 - [23:49:10] <lambdabot> 1.152921504606847e18 + > encodeFloat 1 (2^31 - 1) + Infinity -- ok @@ -10,16 +11,2 @@ - [23:49:09] <arkeet> > encodeFloat 1 60 - [23:49:10] <lambdabot> 1.152921504606847e18 - [23:49:18] <arkeet> er. - [23:50:21] <bscarlet> down in the sane range I suspect it's just fine. - [23:50:43] <bscarlet> > encodeFloat 1 1000 - [23:50:44] <lambdabot> 1.0715086071862673e301 - [23:50:52] <bscarlet> > encodeFloat 1 10000 - [23:50:53] <lambdabot> Infinity - [23:50:58] <bscarlet> That's sane. - [23:51:03] <arkeet> > encodeFloat 1 (2^31) - [23:51:04] <lambdabot> 0.0 - [23:51:13] <bscarlet> That's what I think is weird. - [23:51:19] <carter> bscarlet floats are weird - [23:51:23] <arkeet> > encodeFloat 1 (2^31-1) - [23:51:24] <lambdabot> Infinity - + > encodeFloat 1 (2^31) + 0.0 -- not ok @@ -27,6 +14,0 @@ - Benjamin did a wee bit of investigation, and the - problem seems to lie in https://github.com/ghc/packages-integer- - gmp/blob/master/cbits/float.c#L177 - in integer-gmp, where it deliberately doesn't handle the edge cases - (probably worth investigating) if integer-simple has similar behavior or - not New description: {{{

encodeFloat 1 1023 8.98846567431158e307 -- ok

encodeFloat 1 1024 Infinity -- ok

encodeFloat 1 (2^31 - 1) Infinity -- ok

encodeFloat 1 (2^31) 0.0 -- not ok }}}

-- Comment (by thomie): I think this just needs an update to the `encodeFloat` docstring. To confirms what hvr said in comment:2: test.c: {{{ #include #include #include #include #include #include void test(double x, int exp) { errno = 0; feclearexcept(FE_ALL_EXCEPT); printf("(%f)*2^(%d) = %f\n", x, exp, ldexp(x, exp)); printf("errno: %d (ERANGE = %d), UNDERFLOW: %d, OVERFLOW: %d\n", errno, ERANGE, fetestexcept(FE_UNDERFLOW) == FE_UNDERFLOW, fetestexcept(FE_OVERFLOW) == FE_OVERFLOW); } void main() { // If the result overflows, a range error occurs, and the functions // return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with a sign // the same as x. test(1, 1024); test(1, INT_MAX); // 2^31 - 1 printf("\n"); // If the result underflows, a range error occurs, and zero is // returned. test(1, DBL_MIN_EXP); // Not sure why not getting range error here, test(1, -1074); // or here. test(1, -1075); // but only starting here. test(1, 1 << 31); printf("\n"); // If x is positive infinity (negative infinity), positive infinity // (negative infinity) is returned. test(HUGE_VAL, 1 << 31); test(- HUGE_VAL, 1 << 31); } }}} {{{ $ gcc test.c -lm $ ./a.out (1.000000)*2^(1024) = inf errno: 34 (ERANGE = 34), UNDERFLOW: 0, OVERFLOW: 1 (1.000000)*2^(2147483647) = inf errno: 34 (ERANGE = 34), UNDERFLOW: 0, OVERFLOW: 1 (1.000000)*2^(-1021) = 0.000000 errno: 0 (ERANGE = 34), UNDERFLOW: 0, OVERFLOW: 0 (1.000000)*2^(-1074) = 0.000000 errno: 0 (ERANGE = 34), UNDERFLOW: 0, OVERFLOW: 0 (1.000000)*2^(-1075) = 0.000000 errno: 34 (ERANGE = 34), UNDERFLOW: 1, OVERFLOW: 0 (1.000000)*2^(-2147483648) = 0.000000 errno: 34 (ERANGE = 34), UNDERFLOW: 1, OVERFLOW: 0 (inf)*2^(-2147483648) = inf errno: 0 (ERANGE = 34), UNDERFLOW: 0, OVERFLOW: 0 (-inf)*2^(-2147483648) = -inf errno: 0 (ERANGE = 34), UNDERFLOW: 0, OVERFLOW: 0 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8285#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler