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Fix tanf spurious underflows (bug 18221).
The flt-32 implementation of tanf produces spurious underflow exceptions for some small arguments, through computing values on the order of x^5. This patch fixes this by adjusting the threshold for returning x (or, as applicable, +/- 1/x) to 2**-13 (the next term in the power series being x^3/3). Tested for x86_64 and x86. [BZ #18221] * sysdeps/ieee754/flt-32/k_tanf.c (__kernel_tanf): Use 2**-13 not 2**-28 as threshold for returning x or +/- 1/x. * math/auto-libm-test-in: Add more tests of tan. * math/auto-libm-test-out: Regenerated.
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Joseph Myers
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@ -1,5 +1,11 @@
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2015-05-15 Joseph Myers <joseph@codesourcery.com>
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[BZ #18221]
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* sysdeps/ieee754/flt-32/k_tanf.c (__kernel_tanf): Use 2**-13 not
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2**-28 as threshold for returning x or +/- 1/x.
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* math/auto-libm-test-in: Add more tests of tan.
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* math/auto-libm-test-out: Regenerated.
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[BZ #18220]
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* sysdeps/ieee754/flt-32/e_lgammaf_r.c (__ieee754_lgammaf_r): Use
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2**26 not 2**58 as threshold for returning x * (log (x) - 1).
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2
NEWS
2
NEWS
@ -17,7 +17,7 @@ Version 2.22
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17999, 18007, 18019, 18020, 18029, 18030, 18032, 18036, 18038, 18039,
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18042, 18043, 18046, 18047, 18068, 18080, 18093, 18100, 18104, 18110,
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18111, 18125, 18128, 18138, 18185, 18196, 18197, 18206, 18210, 18211,
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18217, 18220, 18247, 18287, 18319, 18333, 18346, 18397, 18409.
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18217, 18220, 18221, 18247, 18287, 18319, 18333, 18346, 18397, 18409.
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* Cache information can be queried via sysconf() function on s390 e.g. with
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_SC_LEVEL1_ICACHE_SIZE as argument.
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@ -2418,6 +2418,8 @@ tan pi/4
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tan 0.75
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tan 0x1p65
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tan -0x1p65
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tan 0x1p-27
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tan -0x1p-27
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tan 0xc.9p-4
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tan 0xc.908p-4
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tan 0xc.90cp-4
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@ -186618,6 +186618,56 @@ tan -0x1p65
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= tan tonearest ldbl-128ibm -0x2p+64L : 0xc.17b0bfdb2b8061e7b11d500874p-8L : inexact-ok
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= tan towardzero ldbl-128ibm -0x2p+64L : 0xc.17b0bfdb2b8061e7b11d50087p-8L : inexact-ok
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= tan upward ldbl-128ibm -0x2p+64L : 0xc.17b0bfdb2b8061e7b11d500874p-8L : inexact-ok
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tan 0x1p-27
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= tan downward flt-32 0x2p-28f : 0x2p-28f : inexact-ok
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= tan tonearest flt-32 0x2p-28f : 0x2p-28f : inexact-ok
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= tan towardzero flt-32 0x2p-28f : 0x2p-28f : inexact-ok
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= tan upward flt-32 0x2p-28f : 0x2.000004p-28f : inexact-ok
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= tan downward dbl-64 0x2p-28 : 0x2p-28 : inexact-ok
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= tan tonearest dbl-64 0x2p-28 : 0x2p-28 : inexact-ok
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= tan towardzero dbl-64 0x2p-28 : 0x2p-28 : inexact-ok
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= tan upward dbl-64 0x2p-28 : 0x2.0000000000002p-28 : inexact-ok
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= tan downward ldbl-96-intel 0x2p-28L : 0x2.00000000000002a8p-28L : inexact-ok
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= tan tonearest ldbl-96-intel 0x2p-28L : 0x2.00000000000002acp-28L : inexact-ok
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= tan towardzero ldbl-96-intel 0x2p-28L : 0x2.00000000000002a8p-28L : inexact-ok
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= tan upward ldbl-96-intel 0x2p-28L : 0x2.00000000000002acp-28L : inexact-ok
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= tan downward ldbl-96-m68k 0x2p-28L : 0x2.00000000000002a8p-28L : inexact-ok
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= tan tonearest ldbl-96-m68k 0x2p-28L : 0x2.00000000000002acp-28L : inexact-ok
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= tan towardzero ldbl-96-m68k 0x2p-28L : 0x2.00000000000002a8p-28L : inexact-ok
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= tan upward ldbl-96-m68k 0x2p-28L : 0x2.00000000000002acp-28L : inexact-ok
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= tan downward ldbl-128 0x2p-28L : 0x2.00000000000002aaaaaaaaaaaaaep-28L : inexact-ok
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= tan tonearest ldbl-128 0x2p-28L : 0x2.00000000000002aaaaaaaaaaaaaep-28L : inexact-ok
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= tan towardzero ldbl-128 0x2p-28L : 0x2.00000000000002aaaaaaaaaaaaaep-28L : inexact-ok
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= tan upward ldbl-128 0x2p-28L : 0x2.00000000000002aaaaaaaaaaaabp-28L : inexact-ok
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= tan downward ldbl-128ibm 0x2p-28L : 0x2.00000000000002aaaaaaaaaaaap-28L : inexact-ok
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= tan tonearest ldbl-128ibm 0x2p-28L : 0x2.00000000000002aaaaaaaaaaabp-28L : inexact-ok
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= tan towardzero ldbl-128ibm 0x2p-28L : 0x2.00000000000002aaaaaaaaaaaap-28L : inexact-ok
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= tan upward ldbl-128ibm 0x2p-28L : 0x2.00000000000002aaaaaaaaaaabp-28L : inexact-ok
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tan -0x1p-27
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= tan downward flt-32 -0x2p-28f : -0x2.000004p-28f : inexact-ok
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= tan tonearest flt-32 -0x2p-28f : -0x2p-28f : inexact-ok
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= tan towardzero flt-32 -0x2p-28f : -0x2p-28f : inexact-ok
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= tan upward flt-32 -0x2p-28f : -0x2p-28f : inexact-ok
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= tan downward dbl-64 -0x2p-28 : -0x2.0000000000002p-28 : inexact-ok
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= tan tonearest dbl-64 -0x2p-28 : -0x2p-28 : inexact-ok
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= tan towardzero dbl-64 -0x2p-28 : -0x2p-28 : inexact-ok
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= tan upward dbl-64 -0x2p-28 : -0x2p-28 : inexact-ok
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= tan downward ldbl-96-intel -0x2p-28L : -0x2.00000000000002acp-28L : inexact-ok
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= tan tonearest ldbl-96-intel -0x2p-28L : -0x2.00000000000002acp-28L : inexact-ok
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= tan towardzero ldbl-96-intel -0x2p-28L : -0x2.00000000000002a8p-28L : inexact-ok
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= tan upward ldbl-96-intel -0x2p-28L : -0x2.00000000000002a8p-28L : inexact-ok
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= tan downward ldbl-96-m68k -0x2p-28L : -0x2.00000000000002acp-28L : inexact-ok
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= tan tonearest ldbl-96-m68k -0x2p-28L : -0x2.00000000000002acp-28L : inexact-ok
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= tan towardzero ldbl-96-m68k -0x2p-28L : -0x2.00000000000002a8p-28L : inexact-ok
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= tan upward ldbl-96-m68k -0x2p-28L : -0x2.00000000000002a8p-28L : inexact-ok
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= tan downward ldbl-128 -0x2p-28L : -0x2.00000000000002aaaaaaaaaaaabp-28L : inexact-ok
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= tan tonearest ldbl-128 -0x2p-28L : -0x2.00000000000002aaaaaaaaaaaaaep-28L : inexact-ok
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= tan towardzero ldbl-128 -0x2p-28L : -0x2.00000000000002aaaaaaaaaaaaaep-28L : inexact-ok
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= tan upward ldbl-128 -0x2p-28L : -0x2.00000000000002aaaaaaaaaaaaaep-28L : inexact-ok
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= tan downward ldbl-128ibm -0x2p-28L : -0x2.00000000000002aaaaaaaaaaabp-28L : inexact-ok
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= tan tonearest ldbl-128ibm -0x2p-28L : -0x2.00000000000002aaaaaaaaaaabp-28L : inexact-ok
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= tan towardzero ldbl-128ibm -0x2p-28L : -0x2.00000000000002aaaaaaaaaaaap-28L : inexact-ok
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= tan upward ldbl-128ibm -0x2p-28L : -0x2.00000000000002aaaaaaaaaaaap-28L : inexact-ok
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tan 0xc.9p-4
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= tan downward flt-32 0xc.9p-4f : 0xf.fe04cp-4f : inexact-ok
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= tan tonearest flt-32 0xc.9p-4f : 0xf.fe04dp-4f : inexact-ok
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@ -45,7 +45,7 @@ float __kernel_tanf(float x, float y, int iy)
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int32_t ix,hx;
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GET_FLOAT_WORD(hx,x);
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ix = hx&0x7fffffff; /* high word of |x| */
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if(ix<0x31800000) /* x < 2**-28 */
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if(ix<0x39000000) /* x < 2**-13 */
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{if((int)x==0) { /* generate inexact */
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if((ix|(iy+1))==0) return one/fabsf(x);
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else return (iy==1)? x: -one/x;
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