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

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

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,
+  13824, 13840, 13841, 13844, 13846, 13851, 13852, 13854, 13871, 13872,
-  13879, 13883, 13892, 13895, 13908, 13910, 13911, 13912, 13913, 13915,
+  13873, 13879, 13883, 13892, 13895, 13908, 13910, 13911, 13912, 13913,
-  13916, 13917, 13918, 13919, 13920, 13921, 13926, 13928, 13938, 13963
+  13915, 13916, 13917, 13918, 13919, 13920, 13921, 13926, 13928, 13938,
+  13963
 
 * ISO C11 support:
 

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);
-  TEST_ff_f (pow, 10, -max_value, 0, OVERFLOW_EXCEPTION_OK);
 
   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);
-  TEST_ff_f (pow, -max_value, -max_value, plus_zero, OVERFLOW_EXCEPTION_OK);
 
   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);
-  TEST_ff_f (pow, -min_value, max_value, plus_zero, OVERFLOW_EXCEPTION_OK);
 
 #ifndef TEST_LDOUBLE /* Bug 13881.  */
   TEST_ff_f (pow, 0x0.ffffffp0, 10, 0.999999403953712118183885036774764444747L);

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
+	testb	$2, %dh
-
-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
 	jz	292f
 	// x is negative.  If y is an odd integer, negate the result.
 	fldt	24(%esp)	// y : abs(result)

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
+	testb	$2, %dh
-
-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
 	jz	292f
 	// x is negative.  If y is an odd integer, negate the result.
 	fldt	24(%rsp)	// y : abs(result)