Fix exp(3) for arg Inf and -Inf. From NetBSD; PR 4578. ok deraadt@

1 files changed, 105 insertions, 13 deletions

diff --git a/lib/libm/arch/i387/e_exp.S b/lib/libm/arch/i387/e_exp.S
index bc1b34652cb..e4ec1de95e1 100644
--- a/lib/libm/arch/i387/e_exp.S
+++ b/lib/libm/arch/i387/e_exp.S
@@ -1,35 +1,127 @@
-/*	$OpenBSD: e_exp.S,v 1.5 2005/08/02 11:17:31 espie Exp $ */
+/*	$OpenBSD: e_exp.S,v 1.6 2005/11/15 20:41:35 otto Exp $	*/
+/*	$NetBSD: e_exp.S,v 1.12 2002/02/27 16:32:46 christos Exp $	*/
+
 /*
- * Written by J.T. Conklin <jtc@netbsd.org>.
- * Public domain.
+ * Copyright (c) 1993,94 Winning Strategies, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *      This product includes software developed by Winning Strategies, Inc.
+ * 4. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * Written by:
+ *	J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
  */
 
 #include <machine/asm.h>
 
 /* e^x = 2^(x * log2(e)) */
 ENTRY(__ieee754_exp)
-	subl	$8,%esp
-
-	fstcw	4(%esp)		/* store fpu control word */
-	movw	4(%esp),%dx
+#ifndef __i386__
+	/*
+	 * XXX: This code is broken and needs to be merged with the i386 case.
+	 */
+	fstcw	-12(%rsp)
+	movw	-12(%rsp),%dx
 	orw	$0x0180,%dx
-	movw	%dx,(%esp)
-	fldcw	(%esp)		/* load modfied control word */
+	movw	%dx,-16(%rsp)
+	fldcw	-16(%rsp)
+	movsd	%xmm0,-8(%rsp)
+	fldl	-8(%rsp)
 
-	fldl	12(%esp)
 	fldl2e
 	fmulp				/* x * log2(e) */
-	fst	%st(1)
+	fld	%st(0)
 	frndint				/* int(x * log2(e)) */
 	fxch	%st(1)
 	fsub	%st(1),%st		/* fract(x * log2(e)) */
+	f2xm1				/* 2^(fract(x * log2(e))) - 1 */
+	fld1
+	faddp				/* 2^(fract(x * log2(e))) */
+	fscale				/* e^x */
+	fstp	%st(1)
+
+	fstpl	-8(%rsp)
+	movsd	-8(%rsp),%xmm0
+	fldcw	-12(%rsp)
+	ret
+#else
+	/*
+	 * If x is +-Inf, then the subtraction would give Inf-Inf = NaN.
+	 * Avoid this.  Also avoid it if x is NaN for convenience.
+	 */
+	movl	8(%esp),%eax
+	andl	$0x7fffffff,%eax
+	cmpl	$0x7ff00000,%eax
+	jae	x_Inf_or_NaN
+
+	fldl	4(%esp)
+
+	/*
+	 * Ensure that the rounding mode is to nearest (to give the smallest
+	 * possible fraction) and that the precision is as high as possible.
+	 * We may as well mask interrupts if we switch the mode.
+	 */
+	fstcw	4(%esp)
+	movl	4(%esp),%eax
+	andl	$0x0300,%eax
+	cmpl	$0x0300,%eax		/* RC == 0 && PC == 3? */
+	je	1f			/* jump if mode is good */
+	movl	$0x137f,8(%esp)
+	fldcw	8(%esp)
+1:
+	fldl2e
+	fmulp				/* x * log2(e) */
+	fst	%st(1)
+	frndint				/* int(x * log2(e)) */
+	fst	%st(2)
+	fsubrp				/* fract(x * log2(e)) */
 	f2xm1				/* 2^(fract(x * log2(e))) - 1 */ 
 	fld1
 	faddp				/* 2^(fract(x * log2(e))) */
 	fscale				/* e^x */
 	fstp	%st(1)
+	je	1f
+	fldcw	4(%esp)
+1:
+	ret
 
-	fldcw	4(%esp)		/* restore original control word */
+x_Inf_or_NaN:
+	/*
+	 * Return 0 if x is -Inf.  Otherwise just return x, although the
+	 * C version would return (x + x) (Real Indefinite) if x is a NaN.
+	 */
+	cmpl	$0xfff00000,8(%esp)
+	jne	x_not_minus_Inf
+	cmpl	$0,4(%esp)
+	jne	x_not_minus_Inf
+	fldz
+	ret
 
-	addl	$8,%esp
+x_not_minus_Inf:
+	fldl	4(%esp)
 	ret
+#endif