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

5 files changed, 53 insertions, 33 deletions

diff --git a/ChangeLog b/ChangeLog
index 3686491..a85a1c0 100644
--- 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
--- 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
--- 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
--- 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) == ħinf ?
-	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
--- 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) == ħinf ?
-	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)