linux/arch/m68k/math-emu/fp_log.c
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00

223 lines
3.9 KiB
C

/*
fp_trig.c: floating-point math routines for the Linux-m68k
floating point emulator.
Copyright (c) 1998-1999 David Huggins-Daines / Roman Zippel.
I hereby give permission, free of charge, to copy, modify, and
redistribute this software, in source or binary form, provided that
the above copyright notice and the following disclaimer are included
in all such copies.
THIS SOFTWARE IS PROVIDED "AS IS", WITH ABSOLUTELY NO WARRANTY, REAL
OR IMPLIED.
*/
#include "fp_emu.h"
static const struct fp_ext fp_one =
{
.exp = 0x3fff,
};
extern struct fp_ext *fp_fadd(struct fp_ext *dest, const struct fp_ext *src);
extern struct fp_ext *fp_fdiv(struct fp_ext *dest, const struct fp_ext *src);
extern struct fp_ext *fp_fmul(struct fp_ext *dest, const struct fp_ext *src);
struct fp_ext *
fp_fsqrt(struct fp_ext *dest, struct fp_ext *src)
{
struct fp_ext tmp, src2;
int i, exp;
dprint(PINSTR, "fsqrt\n");
fp_monadic_check(dest, src);
if (IS_ZERO(dest))
return dest;
if (dest->sign) {
fp_set_nan(dest);
return dest;
}
if (IS_INF(dest))
return dest;
/*
* sqrt(m) * 2^(p) , if e = 2*p
* sqrt(m*2^e) =
* sqrt(2*m) * 2^(p) , if e = 2*p + 1
*
* So we use the last bit of the exponent to decide wether to
* use the m or 2*m.
*
* Since only the fractional part of the mantissa is stored and
* the integer part is assumed to be one, we place a 1 or 2 into
* the fixed point representation.
*/
exp = dest->exp;
dest->exp = 0x3FFF;
if (!(exp & 1)) /* lowest bit of exponent is set */
dest->exp++;
fp_copy_ext(&src2, dest);
/*
* The taylor row arround a for sqrt(x) is:
* sqrt(x) = sqrt(a) + 1/(2*sqrt(a))*(x-a) + R
* With a=1 this gives:
* sqrt(x) = 1 + 1/2*(x-1)
* = 1/2*(1+x)
*/
fp_fadd(dest, &fp_one);
dest->exp--; /* * 1/2 */
/*
* We now apply the newton rule to the function
* f(x) := x^2 - r
* which has a null point on x = sqrt(r).
*
* It gives:
* x' := x - f(x)/f'(x)
* = x - (x^2 -r)/(2*x)
* = x - (x - r/x)/2
* = (2*x - x + r/x)/2
* = (x + r/x)/2
*/
for (i = 0; i < 9; i++) {
fp_copy_ext(&tmp, &src2);
fp_fdiv(&tmp, dest);
fp_fadd(dest, &tmp);
dest->exp--;
}
dest->exp += (exp - 0x3FFF) / 2;
return dest;
}
struct fp_ext *
fp_fetoxm1(struct fp_ext *dest, struct fp_ext *src)
{
uprint("fetoxm1\n");
fp_monadic_check(dest, src);
if (IS_ZERO(dest))
return dest;
return dest;
}
struct fp_ext *
fp_fetox(struct fp_ext *dest, struct fp_ext *src)
{
uprint("fetox\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_ftwotox(struct fp_ext *dest, struct fp_ext *src)
{
uprint("ftwotox\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_ftentox(struct fp_ext *dest, struct fp_ext *src)
{
uprint("ftentox\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_flogn(struct fp_ext *dest, struct fp_ext *src)
{
uprint("flogn\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_flognp1(struct fp_ext *dest, struct fp_ext *src)
{
uprint("flognp1\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_flog10(struct fp_ext *dest, struct fp_ext *src)
{
uprint("flog10\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_flog2(struct fp_ext *dest, struct fp_ext *src)
{
uprint("flog2\n");
fp_monadic_check(dest, src);
return dest;
}
struct fp_ext *
fp_fgetexp(struct fp_ext *dest, struct fp_ext *src)
{
dprint(PINSTR, "fgetexp\n");
fp_monadic_check(dest, src);
if (IS_INF(dest)) {
fp_set_nan(dest);
return dest;
}
if (IS_ZERO(dest))
return dest;
fp_conv_long2ext(dest, (int)dest->exp - 0x3FFF);
fp_normalize_ext(dest);
return dest;
}
struct fp_ext *
fp_fgetman(struct fp_ext *dest, struct fp_ext *src)
{
dprint(PINSTR, "fgetman\n");
fp_monadic_check(dest, src);
if (IS_ZERO(dest))
return dest;
if (IS_INF(dest))
return dest;
dest->exp = 0x3FFF;
return dest;
}