Fix spurious overflow exceptions from x86/x86_64 powl (bug 13872).

diff --git a/ChangeLog b/ChangeLog
index 3686491..a85a1c0 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 2012-04-09  Joseph Myers  <joseph@codesourcery.com>
 
+       [BZ #13872]
+       * sysdeps/i386/fpu/e_powl.S (p78): New object.
+       (__ieee754_powl): Saturate large exponents rather than testing for
+       overflow of y*log2(x).
+       * sysdeps/x86_64/fpu/e_powl.S: Likewise.
+       * math/libm-test.inc (pow_test): Do not permit spurious overflow
+       exceptions.
+
        [BZ #11521]
        * math/s_ctan.c: Include <float.h>.
        (__ctan): Avoid internal overflow or cancellation in calculating

diff --git a/NEWS b/NEWS
index bb303f8..357f3b4 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -18,9 +18,10 @@ Version 2.16
   13530, 13531, 13532, 13533, 13547, 13551, 13552, 13553, 13555, 13559,
   13566, 13583, 13592, 13618, 13637, 13656, 13658, 13673, 13691, 13695,
   13704, 13705, 13706, 13726, 13738, 13760, 13761, 13786, 13792, 13806,
-  13824, 13840, 13841, 13844, 13846, 13851, 13852, 13854, 13871, 13873,
-  13879, 13883, 13892, 13895, 13908, 13910, 13911, 13912, 13913, 13915,
-  13916, 13917, 13918, 13919, 13920, 13921, 13926, 13928, 13938, 13963
+  13824, 13840, 13841, 13844, 13846, 13851, 13852, 13854, 13871, 13872,
+  13873, 13879, 13883, 13892, 13895, 13908, 13910, 13911, 13912, 13913,
+  13915, 13916, 13917, 13918, 13919, 13920, 13921, 13926, 13928, 13938,
+  13963
 
 * ISO C11 support:
 

diff --git a/math/libm-test.inc b/math/libm-test.inc
index a551b9f..2809d57 100644 (file)
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -5682,8 +5682,7 @@ pow_test (void)
   TEST_ff_f (pow, 0x1p72L, 0x1p72L, plus_infty, OVERFLOW_EXCEPTION);
   TEST_ff_f (pow, 10, -0x1p72L, 0);
   TEST_ff_f (pow, max_value, max_value, plus_infty, OVERFLOW_EXCEPTION);
-  /* Bug 13872: spurious OVERFLOW exception may be present.  */
-  TEST_ff_f (pow, 10, -max_value, 0, OVERFLOW_EXCEPTION_OK);
+  TEST_ff_f (pow, 10, -max_value, 0);
 
   TEST_ff_f (pow, 0, 1, 0);
   TEST_ff_f (pow, 0, 11, 0);
@@ -5997,8 +5996,7 @@ pow_test (void)
   TEST_ff_f (pow, -max_value, -0x1.ffffffffffffffffffffffffffffp+113L, plus_zero);
 # endif
 #endif
-  /* Bug 13872: spurious OVERFLOW exception may be present.  */
-  TEST_ff_f (pow, -max_value, -max_value, plus_zero, OVERFLOW_EXCEPTION_OK);
+  TEST_ff_f (pow, -max_value, -max_value, plus_zero);
 
   TEST_ff_f (pow, -max_value, 0xffffff, minus_infty, OVERFLOW_EXCEPTION);
   TEST_ff_f (pow, -max_value, 0x1fffffe, plus_infty, OVERFLOW_EXCEPTION);
@@ -6122,8 +6120,7 @@ pow_test (void)
   TEST_ff_f (pow, -min_value, 0x1.ffffffffffffffffffffffffffffp+113L, plus_zero);
 # endif
 #endif
-  /* Bug 13872: spurious OVERFLOW exception may be present.  */
-  TEST_ff_f (pow, -min_value, max_value, plus_zero, OVERFLOW_EXCEPTION_OK);
+  TEST_ff_f (pow, -min_value, max_value, plus_zero);
 
 #ifndef TEST_LDOUBLE /* Bug 13881.  */
   TEST_ff_f (pow, 0x0.ffffffp0, 10, 0.999999403953712118183885036774764444747L);

diff --git a/sysdeps/i386/fpu/e_powl.S b/sysdeps/i386/fpu/e_powl.S
index 0e7c05b..5b166ea 100644 (file)
--- a/sysdeps/i386/fpu/e_powl.S
+++ b/sysdeps/i386/fpu/e_powl.S
@@ -35,6 +35,9 @@ p63:  .byte 0, 0, 0, 0, 0, 0, 0xe0, 0x43
        ASM_TYPE_DIRECTIVE(p64,@object)
 p64:   .byte 0, 0, 0, 0, 0, 0, 0xf0, 0x43
        ASM_SIZE_DIRECTIVE(p64)
+       ASM_TYPE_DIRECTIVE(p78,@object)
+p78:   .byte 0, 0, 0, 0, 0, 0, 0xd0, 0x44
+       ASM_SIZE_DIRECTIVE(p78)
 
        .section .rodata.cst16,"aM",@progbits,16
 
@@ -166,6 +169,21 @@ ENTRY(__ieee754_powl)
        fxch                    // x : y
        fabs                    // |x| : y
        fxch                    // y : |x|
+       // If y has absolute value at least 1L<<78, then any finite
+       // nonzero x will result in 0 (underflow), 1 or infinity (overflow).
+       // Saturate y to those bounds to avoid overflow in the calculation
+       // of y*log2(x).
+       fld     %st             // y : y : |x|
+       fabs                    // |y| : y : |x|
+       fcompl  MO(p78)         // y : |x|
+       fnstsw
+       sahf
+       jc      3f
+       fstp    %st(0)          // pop y
+       fldl    MO(p78)         // 1L<<78 : |x|
+       testb   $2, %dl
+       jz      3f              // y > 0
+       fchs                    // -(1L<<78) : |x|
        .align ALIGNARG(4)
 3:     /* y is a real number.  */
        fxch                    // x : y
@@ -185,11 +203,6 @@ ENTRY(__ieee754_powl)
 
 7:     fyl2x                   // log2(x) : y
 8:     fmul    %st(1)          // y*log2(x) : y
-       fxam
-       fnstsw
-       andb    $0x45, %ah
-       cmpb    $0x05, %ah      // is y*log2(x) == ±inf ?
-       je      28f
        fst     %st(1)          // y*log2(x) : y*log2(x)
        frndint                 // int(y*log2(x)) : y*log2(x)
        fsubr   %st, %st(1)     // int(y*log2(x)) : fract(y*log2(x))
@@ -198,13 +211,7 @@ ENTRY(__ieee754_powl)
        faddl   MO(one)         // 2^fract(y*log2(x)) : int(y*log2(x))
        fscale                  // 2^fract(y*log2(x))*2^int(y*log2(x)) : int(y*log2(x))
        fstp    %st(1)          // 2^fract(y*log2(x))*2^int(y*log2(x))
-       jmp     29f
-
-28:    fstp    %st(1)          // y*log2(x)
-       fldl    MO(one)         // 1 : y*log2(x)
-       fscale                  // 2^(y*log2(x)) : y*log2(x)
-       fstp    %st(1)          // 2^(y*log2(x))
-29:    testb   $2, %dh
+       testb   $2, %dh
        jz      292f
        // x is negative.  If y is an odd integer, negate the result.
        fldt    24(%esp)        // y : abs(result)

diff --git a/sysdeps/x86_64/fpu/e_powl.S b/sysdeps/x86_64/fpu/e_powl.S
index 0626ce4..10ede22 100644 (file)
--- a/sysdeps/x86_64/fpu/e_powl.S
+++ b/sysdeps/x86_64/fpu/e_powl.S
@@ -35,6 +35,9 @@ p63:  .byte 0, 0, 0, 0, 0, 0, 0xe0, 0x43
        ASM_TYPE_DIRECTIVE(p64,@object)
 p64:   .byte 0, 0, 0, 0, 0, 0, 0xf0, 0x43
        ASM_SIZE_DIRECTIVE(p64)
+       ASM_TYPE_DIRECTIVE(p78,@object)
+p78:   .byte 0, 0, 0, 0, 0, 0, 0xd0, 0x44
+       ASM_SIZE_DIRECTIVE(p78)
 
        .section .rodata.cst16,"aM",@progbits,16
 
@@ -151,6 +154,21 @@ ENTRY(__ieee754_powl)
        fxch                    // x : y
        fabs                    // |x| : y
        fxch                    // y : |x|
+       // If y has absolute value at least 1L<<78, then any finite
+       // nonzero x will result in 0 (underflow), 1 or infinity (overflow).
+       // Saturate y to those bounds to avoid overflow in the calculation
+       // of y*log2(x).
+       fldl    MO(p78)         // 1L<<78 : y : |x|
+       fld     %st(1)          // y : 1L<<78 : y : |x|
+       fabs                    // |y| : 1L<<78 : y : |x|
+       fcomip  %st(1), %st     // 1L<<78 : y : |x|
+       fstp    %st(0)          // y : |x|
+       jc      3f
+       fstp    %st(0)          // pop y
+       fldl    MO(p78)         // 1L<<78 : |x|
+       testb   $2, %dl
+       jz      3f              // y > 0
+       fchs                    // -(1L<<78) : |x|
        .align ALIGNARG(4)
 3:     /* y is a real number.  */
        fxch                    // x : y
@@ -170,11 +188,6 @@ ENTRY(__ieee754_powl)
 
 7:     fyl2x                   // log2(x) : y
 8:     fmul    %st(1)          // y*log2(x) : y
-       fxam
-       fnstsw
-       andb    $0x45, %ah
-       cmpb    $0x05, %ah      // is y*log2(x) == ±inf ?
-       je      28f
        fst     %st(1)          // y*log2(x) : y*log2(x)
        frndint                 // int(y*log2(x)) : y*log2(x)
        fsubr   %st, %st(1)     // int(y*log2(x)) : fract(y*log2(x))
@@ -183,13 +196,7 @@ ENTRY(__ieee754_powl)
        faddl   MO(one)         // 2^fract(y*log2(x)) : int(y*log2(x))
        fscale                  // 2^fract(y*log2(x))*2^int(y*log2(x)) : int(y*log2(x))
        fstp    %st(1)          // 2^fract(y*log2(x))*2^int(y*log2(x))
-       jmp     29f
-
-28:    fstp    %st(1)          // y*log2(x)
-       fldl    MO(one)         // 1 : y*log2(x)
-       fscale                  // 2^(y*log2(x)) : y*log2(x)
-       fstp    %st(1)          // 2^(y*log2(x))
-29:    testb   $2, %dh
+       testb   $2, %dh
        jz      292f
        // x is negative.  If y is an odd integer, negate the result.
        fldt    24(%rsp)        // y : abs(result)