/*-------------------------------------------------------------------------
logf.c - Computes the natural log of a 32 bit float as outlined in [1].
Copyright (C) 2001, 2002, Jesus Calvino-Fraga, jesusc@ieee.org
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this library; see the file COPYING. If not, write to the
Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA.
As a special exception, if you link this library with other files,
some of which are compiled with SDCC, to produce an executable,
this library does not by itself cause the resulting executable to
be covered by the GNU General Public License. This exception does
not however invalidate any other reasons why the executable file
might be covered by the GNU General Public License.
-------------------------------------------------------------------------*/
/* [1] William James Cody and W. M. Waite. _Software manual for the
elementary functions_, Englewood Cliffs, N.J.:Prentice-Hall, 1980. */
/* Version 1.0 - Initial release */
#define __SDCC_MATH_LIB
#include <math.h>
#include <errno.h>
#ifdef MATH_ASM_MCS51
#define __SDCC_FLOAT_LIB
#include <float.h>
// TODO: share with other temps
static __data unsigned char logf_tmp[4];
float logf(float x)
{
x;
__asm
// extract the two input, placing it into:
// sign exponent mantiassa
// ---- -------- ---------
// x: sign_a exp_a r4/r3/r2
lcall fsgetarg
logf_neg_check:
jnb sign_a, logf_zero_check
// TODO: set errno to EDOM (negative numbers not allowed)
lcall fs_return_nan
ljmp logf_exit
logf_zero_check:
cjne r4, #0, logf_ok
// TODO: set errno to ERANGE (zero not allowed)
setb sign_a
lcall fs_return_inf
ljmp logf_exit
logf_ok:
push exp_a
mov a, #3
mov r1, #0
lcall fs_rshift_a
clr a
mov (_logf_tmp + 0), a // y = 0
mov (_logf_tmp + 1), a
mov (_logf_tmp + 2), a
mov (_logf_tmp + 3), a
mov dptr, #__fs_natural_log_table
mov r0, a
logf_cordic_loop:
mov ar7, r4 // r7/r6/r5 = x >> i
mov ar6, r3
mov ar5, r2
mov b, r1
mov a, r0
lcall __fs_cordic_rshift_r765_unsigned
mov a, r1 // check if x + (x >> i) > 1.0
add a, b
mov a, r2
addc a, r5
mov a, r3
addc a, r6
mov a, r4
addc a, r7
anl a, #0xE0
jnz logf_cordic_skip
mov a, r1 // x = x + (x >> i)
add a, b
mov r1, a
mov a, r2
addc a, r5
mov r2, a
mov a, r3
addc a, r6
mov r3, a
mov a, r4
addc a, r7
mov r4, a
clr a // y = y + log_table[i]
movc a, @a+dptr
add a, (_logf_tmp + 0)
mov (_logf_tmp + 0), a
mov a, #1
movc a, @a+dptr
addc a, (_logf_tmp + 1)
mov (_logf_tmp + 1), a
mov a, #2
movc a, @a+dptr
addc a, (_logf_tmp + 2)
mov (_logf_tmp + 2), a
mov a, #3
movc a, @a+dptr
addc a, (_logf_tmp + 3)
mov (_logf_tmp + 3), a
logf_cordic_skip:
inc dptr
inc dptr
inc dptr
inc dptr
inc r0
cjne r0, #30, logf_cordic_loop
// at this point, _logf_tmp has the natural log of the positive
// normalized fractional part (0.5 to 1.0 -> 0.693 to 0.0)
mov r4, (_logf_tmp + 3)
mov r3, (_logf_tmp + 2)
mov r2, (_logf_tmp + 1)
mov r1, (_logf_tmp + 0)
mov exp_a, #129
setb sign_a
lcall fs_normalize_a
pop acc
cjne a, #126, logf_exponent
// if the input exponent was 126, then we don't need to add
// anything and we can just return the with we have already
// TODO: which of these gives best accuracy???
lcall fs_zerocheck_return
//lcall fs_round_and_return
sjmp logf_exit
logf_exponent:
jc logf_exp_neg
// the input exponent was greater than 126
logf_exp_pos:
add a, #130
clr sign_b
sjmp logf_exp_scale
logf_exp_neg:
// the input exponent was less than 126
cpl a
add a, #127
setb sign_b
logf_exp_scale:
// r0 has abs(exp - 126)
mov r0, a
// put the log of faction into b, so we can use a to compute
// the offset to be added to it or subtracted from it
lcall fs_swap_a_b
// multiply r0 by log(2), or r0 * 0xB17218
mov a, #0x18
mov b, r0
mul ab
mov r1, a
mov r2, b
mov a, #0xB1
mov b, r0
mul ab
mov r3, a
mov r4, b
mov a, #0x72
mov b, r0
mul ab
add a, r2
mov r2, a
mov a, b
addc a, r3
mov r3, a
clr a
addc a, r4
mov r4, a
// turn r0 * log(2) into a proper float
mov exp_a, #134
lcall fs_normalize_a
// now just add log(fractional) +/- log(2) * abs(exp - 126)
lcall fsadd_direct_entry
logf_exit:
__endasm;
#pragma less_pedantic
}
#else // not MATH_ASM_MCS51
/*Constants for 24 bits or less (8 decimal digits)*/
#define A0 -0.5527074855E+0
#define B0 -0.6632718214E+1
#define A(w) (A0)
#define B(w) (w+B0)
#define C0 0.70710678118654752440
#define C1 0.693359375 /*355.0/512.0*/
#define C2 -2.121944400546905827679E-4
float logf(float x) _FLOAT_FUNC_REENTRANT
{
#if defined(__SDCC_mcs51) && defined(__SDCC_MODEL_SMALL) \
&& !defined(__SDCC_NOOVERLAY)
volatile
#endif
float Rz;
float f, z, w, znum, zden, xn;
int n;
if (x<=0.0)
{
errno=EDOM;
return 0.0;
}
f=frexpf(x, &n);
znum=f-0.5;
if (f>C0)
{
znum-=0.5;
zden=(f*0.5)+0.5;
}
else
{
n--;
zden=znum*0.5+0.5;
}
z=znum/zden;
w=z*z;
Rz=z+z*(w*A(w)/B(w));
xn=n;
return ((xn*C2+Rz)+xn*C1);
}
#endif