eb7e930697
The log message for 1.5 said that some small (one or two ulp) inaccuracies were fixed, and a comment implied that the critical change is to switch the rounding mode to to-nearest, with a switch of the precision to extended at no extra cost. Actually, the errors are very large (ucbtest finds ones of several hundred ulps), and it is the switch of the precision that is critical. Another comment was wrong about NaNs being handled sloppily.
99 lines
3.0 KiB
ArmAsm
99 lines
3.0 KiB
ArmAsm
/*
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* Copyright (c) 1993,94 Winning Strategies, Inc.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by Winning Strategies, Inc.
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* 4. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Written by:
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* J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
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*/
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#include <machine/asm.h>
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RCSID("$FreeBSD$")
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/* e^x = 2^(x * log2(e)) */
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ENTRY(exp)
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/*
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* If x is +-Inf, then the subtraction would give Inf-Inf = NaN.
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* Avoid this. Also avoid it if x is NaN for convenience.
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*/
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movl 8(%esp),%eax
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andl $0x7fffffff,%eax
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cmpl $0x7ff00000,%eax
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jae x_Inf_or_NaN
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fldl 4(%esp)
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/*
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* Extended precision is needed to reduce the maximum error from
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* hundreds of ulps to less than 1 ulp. Switch to it if necessary.
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* We may as well set the rounding mode to to-nearest and mask traps
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* if we switch.
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*/
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fstcw 4(%esp)
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movl 4(%esp),%eax
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andl $0x0300,%eax
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cmpl $0x0300,%eax /* RC == 0 && PC == 3? */
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je 1f /* jump if mode is good */
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movl $0x137f,8(%esp)
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fldcw 8(%esp)
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1:
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fldl2e
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fmulp /* x * log2(e) */
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fst %st(1)
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frndint /* int(x * log2(e)) */
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fst %st(2)
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fsubrp /* fract(x * log2(e)) */
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f2xm1 /* 2^(fract(x * log2(e))) - 1 */
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fld1
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faddp /* 2^(fract(x * log2(e))) */
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fscale /* e^x */
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fstp %st(1)
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je 1f
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fldcw 4(%esp)
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1:
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ret
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x_Inf_or_NaN:
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/*
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* Return 0 if x is -Inf. Otherwise just return x; when x is Inf
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* this gives Inf, and when x is a NaN this gives the same result
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* as (x + x) (x quieted).
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*/
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cmpl $0xfff00000,8(%esp)
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jne x_not_minus_Inf
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cmpl $0,4(%esp)
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jne x_not_minus_Inf
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fldz
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ret
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x_not_minus_Inf:
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fldl 4(%esp)
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ret
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