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/* -*- Mode: Asm -*- */
/* Copyright (c) 2002 Michael Stumpf <mistumpf@de.pepperl-fuchs.com>
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* 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.
* Neither the name of the copyright holders nor the names of
contributors may be used to endorse or promote products derived
from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
*/
/*
tanh.S is part of FPlib V 0.3.0 ported to avr-as
for details see readme.fplib
*----------------------------------------------------------------------------------------
*
* A = tanh(A)
*
* tanh( x ) = sinh(x)/cosh(x)
* (exp(x) - exp(-x)) 1 - exp(-2x) (exp(2x) - 1
* = ------------------- = ------------- = -------------
* (exp(x) + exp(-x)) = 1 + exp(-2x) (exp(2x) + 1
*
* if exp(x) +- exp(-x) == exp(x) => exp(2x) +- 1 == exp(2x) => exp(2x) >= 2^24 -> x = ln(2^24)/2
*/
#if !defined(DOXYGEN)
#include "gasava.inc"
#include "fplib.inc"
TEXT_SEG(fplib, tanh)
FUNCTION(tanh)
GLOBAL(tanh)
/* check for x > 8.3177661895751953 [41051592]
*/
BST rA3,7
ANDI rA3,0x7F
LDI rB3,0x41
LDI rB2,0x05
LDI rB1,0x15
CPI rA0,0x92+1
CPC rA1,rB1
CPC rA2,rB2
CPC rA3,rB3 ; compare with 8.3177661895751953 = | ln(2^24)/2 |
BRCS _tanh_00
LDI rA3,0x3F
LDI rA2,0x80
LDI rA1,0x00
LDI rA0,0x00 ; load 1
BLD rA3,7 ; if x positivive _tanh(x) = 1
RET
_tanh_00:
BLD rA3,7
PUSH rA0 /* LDI rB3,1 */
PUSH rA1 /* RCALL _ldexp ; x -> 2x */
PUSH rA2 /* */
PUSH rA3 /* RCALL _exp */
RCALL _U(cosh) /* PUSH rA0 */
POP rB3 /* PUSH rA1 */
POP rB2 /* PUSH rA2 */
POP rB1 /* PUSH rA3 */
POP rB0 /* CLR rB0 */
PUSH rA3 /* CLR rB1 */
PUSH rA2 /* LDI rB2,0x80 */
PUSH rA1 /* LDI rB3,0x3F ; B = 1.0 */
PUSH rA0 /* RCALL ___addsf3 */
MOV rA3,rB3 /* POP rB3 */
MOV rA2,rB2 /* POP rB2 */
MOV rA1,rB1 /* POP rB1 */
MOV rA0,rB0 /* POP rB0 ; B = exp(2x) */
RCALL _U(sinh) /* PUSH rA0 */
POP rB0 /* PUSH rA1 */
POP rB1 /* PUSH rA2 */
POP rB2 /* PUSH rA3 */
POP rB3 /* CLR rA0 */
RJMP _U(__divsf3) /* CLR rA1 */
/* LDI rA2,0x80 */
/* LDI rA3,0xBF ; A = -1.0 */
/* RCALL ___addsf3 */
/* POP rB3 */
/* POP rB2 */
/* POP rB1 */
/* POP rB0 ; B = exp(2x)+1 */
/* RJMP ___divsf3 */
ENDFUNC
#endif /* not DOXYGEN */
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