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authorUlrich Drepper <drepper@redhat.com>1999-07-14 00:54:57 +0000
committerUlrich Drepper <drepper@redhat.com>1999-07-14 00:54:57 +0000
commitabfbdde177c3a7155070dda1b2cdc8292054cc26 (patch)
treee021306b596381fbf8311d2b7eb294e918ff17c8 /sysdeps/i386/fpu/e_expf.S
parent86421aa57ecfd70963ae66848bd6a6dd3b8e0fe6 (diff)
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+/*
+ * Written by J.T. Conklin <jtc@netbsd.org>.
+ * Public domain.
+ * Adapted for float type by Ulrich Drepper <drepper@cygnus.com>.
+ */
+
+#include <machine/asm.h>
+
+RCSID("$NetBSD: $")
+
+/* e^x = 2^(x * log2(e)) */
+ENTRY(__ieee754_expf)
+	flds	4(%esp)
+/* I added the following ugly construct because exp(+-Inf) resulted
+   in NaN.  The ugliness results from the bright minds at Intel.
+   For the i686 the code can be written better.
+   -- drepper@cygnus.com.  */
+	fxam				/* Is NaN or +-Inf?  */
+	fstsw	%ax
+	movb	$0x45, %dh
+	andb	%ah, %dh
+	cmpb	$0x05, %dh
+	je	1f			/* Is +-Inf, jump.  */
+	fldl2e
+	fmulp				/* x * log2(e) */
+	fld	%st
+	frndint				/* int(x * log2(e)) */
+	fsubr	%st,%st(1)		/* fract(x * log2(e)) */
+	fxch
+	f2xm1				/* 2^(fract(x * log2(e))) - 1 */
+	fld1
+	faddp				/* 2^(fract(x * log2(e))) */
+	fscale				/* e^x */
+	fstp	%st(1)
+	ret
+
+1:	testl	$0x200, %eax		/* Test sign.  */
+	jz	2f			/* If positive, jump.  */
+	fstp	%st
+	fldz				/* Set result to 0.  */
+2:	ret
+END (__ieee754_expf)