On x86, glibc's sin(0x1p1023) returns: -0.633004553570852834809556952677667140960693359375 The correct value (rounded to double precision, within 1ulp) is: 0.563127779850884024881452205590903759002685546875 Or, rounded to the DBL_DIG digits (15): 0.563127779850884 In case there's any doubt as to the true value, it agrees with Wolfram Alpha's estimate of sin(2^1023), which is: 0.5631277798508840134529434079444683477103854907361251 Source: http://www.wolframalpha.com/input/?i=sin%282%5E1023%29 Apparently glibc's trig functions are failing to perform argument reduction in any sane way...
This is a duplicate of bug#13658. I'll add your test case to the testsuite. *** This bug has been marked as a duplicate of bug 13658 ***