__expo2 cleanup

[libm] / src / math / __expo2f.c

diff --git a/src/math/__expo2f.c b/src/math/__expo2f.c
index 192838f..d35f440 100644 (file)
--- a/src/math/__expo2f.c
+++ b/src/math/__expo2f.c
@@ -1,51 +1,16 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/k_expf.c */
-/*-
- * Copyright (c) 2011 David Schultz <das@FreeBSD.ORG>
- * 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.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
- */
-
 #include "libm.h"
 
-/*
- * We use exp(x) = exp(x - kln2) * 2**k,
- * k is carefully chosen to minimize |exp(kln2) - 2**k|
- */
+/* k minimizes |exp(k ln2) - 2**k|, see cmath/__cexpf.c */
 static const uint32_t k = 235;
 static const float kln2 = 162.88958740f;
 
-/* expf(x)/2 when x is huge */
+/* expf(x)/2 for large x */
 float __expo2f(float x)
 {
        float scale;
-       int n;
 
-       /*
-        * efficient scalbnf(y, k-1):
-        * 2**(k-1) cannot be represented
-        * so we use that k-1 is even and scale in two steps
-        */
-       n = (k - 1)/2;
-       SET_FLOAT_WORD(scale, (0x7f + n) << 23);
+       /* note that k is odd and scale*scale overflows */
+       SET_FLOAT_WORD(scale, (0x7f + k/2) << 23);
+       /* exp(x - k ln2) * 2**(k-1) */
        return expf(x - kln2) * scale * scale;
 }