From 600fa36158cd741d897b2d22c735c60247b982e0 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Tue, 11 Mar 2014 22:24:00 +0000 Subject: Fix nextafter overflow in non-default rounding modes (bug 16677). ISO C requires the result of nextafter to be independent of the rounding mode, even when underflow or overflow occurs. This patch fixes the bug in various nextafter implementations that, having done an overflowing computation to force an overflow exception (correct), they then return the result of that computation rather than an infinity computed some other way (incorrect, when the overflowing result of arithmetic with that sign and rounding mode is finite but the correct result is infinite) - generally by falling through to existing code to return a value that in fact is correct for this case (but was computed by an integer increment and so without generating the exceptions required). Having fixed the bug, the previously deferred conversion of nextafter testing in libm-test.inc to ALL_RM_TEST is also included. Tested x86_64 and x86; also spot-checked results of nextafter tests for powerpc32 and mips64 to test the ldbl-128ibm and ldbl-128 changes. (The m68k change is untested.) [BZ #16677] * math/s_nextafter.c (__nextafter): Do not return value from overflowing computation. * sysdeps/i386/fpu/s_nextafterl.c (__nextafterl): Likewise. * sysdeps/ieee754/flt-32/s_nextafterf.c (__nextafterf): Likewise. * sysdeps/ieee754/ldbl-128/s_nextafterl.c (__nextafterl): Likewise. * sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl): Likewise. * sysdeps/m68k/m680x0/fpu/s_nextafterl.c (__nextafterl): Likewise. * math/libm-test.inc (nextafter_test): Use ALL_RM_TEST. --- sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) (limited to 'sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c') diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c b/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c index c050944..30b1540 100644 --- a/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c +++ b/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c @@ -66,8 +66,11 @@ long double __nextafterl(long double x, long double y) long double with a 106 bit mantissa, and nextafterl is insane with variable precision. So to make nextafterl sane we assume 106 bit precision. */ - if((hx==0xffefffffffffffffLL)&&(lx==0xfc8ffffffffffffeLL)) - return x+x; /* overflow, return -inf */ + if((hx==0xffefffffffffffffLL)&&(lx==0xfc8ffffffffffffeLL)) { + u = x+x; /* overflow, return -inf */ + math_force_eval (u); + return y; + } if (hx >= 0x7ff0000000000000LL) { u = 0x1.fffffffffffff7ffffffffffff8p+1023L; return u; @@ -93,8 +96,11 @@ long double __nextafterl(long double x, long double y) } return x - u; } else { /* x < y, x += ulp */ - if((hx==0x7fefffffffffffffLL)&&(lx==0x7c8ffffffffffffeLL)) - return x+x; /* overflow, return +inf */ + if((hx==0x7fefffffffffffffLL)&&(lx==0x7c8ffffffffffffeLL)) { + u = x+x; /* overflow, return +inf */ + math_force_eval (u); + return y; + } if ((uint64_t) hx >= 0xfff0000000000000ULL) { u = -0x1.fffffffffffff7ffffffffffff8p+1023L; return u; -- cgit v1.1