替换'pow（）'功能 [英] replacement for 'pow()' function
问题描述
你好，
我想简单地替换嵌入式
平台的''pow（）''函数我'正在努力。什么是更好的方式，可能有点转移？
谢谢。
祝你好运，Roman Mashak。
Hello,
I''d like to make a simple replacement of ''pow()'' function for the embedded
platform I''m working on. What is the better way, probably bit shifting?
Thanks.
Best regards, Roman Mashak.
推荐答案
Roman Mashak写道，在12/12/07 00:43：
Roman Mashak wrote, On 14/12/07 00:43:
你好，
我想为我正在研究的嵌入式
平台简单地替换''pow（）''函数。什么是更好的方式，可能是位移？
谢谢。
Hello,
I''d like to make a simple replacement of ''pow()'' function for the embedded
platform I''m working on. What is the better way, probably bit shifting?
Thanks.
这一切都取决于您的要求的详细信息，包括
速度，准确度或空间是否更重要以及每个的限制。我知道代码使用了一个小型查找表来执行trig函数，一个
导致很多不准确但它足够好，快速很小。
我知道其他代码使用查找表和一些
形式的插值（我从未检查过细节）因为速度有点小
很重要（处理器更快）。
-
Flash Gordon
It all depends on the details of your requirements, including whether
speed, accuracy or space is more important and on the limits for each. I
know of code that uses a small look-up-table for trig functions, one
that leads to a lot of inaccuracy but it "good enough", fast and small.
I know other code that uses a look-up-table and interpolation of some
form (I never checked the details) because speed was a bit less
important (the processor was faster).
--
Flash Gordon
Roman Mashak写道：
Roman Mashak wrote:
>
您好，
我想要为我正在研究的嵌入式平台做一个简单的替换''pow（）''
函数。
>
Hello,
I''d like to make a simple replacement of ''pow()''
function for the embedded platform I''m working on.
/ * BEGIN fs_pow_test.c * /
#include< stdio.h>
/ *
** fs_pow以便携式独立代码实现
* /
#include" fs_pow.h"
int main（无效）
{
puts（" / * BEGIN fs_pow_test.c output * / \ n"）;
printf（" fs_pow（2,4）is％f\\\
\ n"，
fs_pow（2,4））;
printf（" fs_pow（0.0001，-0.25） - 10是％e \ n \ nn"，
fs_pow（0.0001，-0.25） - 10）;
puts（" / * END fs_pow_test.c输出* /"）;
返回0;
}
/ * END fs_pow_test.c * /
/ * BEGIN fs_pow.h * /
/ *
* *可独立或托管的便携代码
**实施C.
* /
#ifndef H_FS_POW_H
#define H_FS_POW_H
double fs_pow（double x，double y）;
double fs_fmod（d ouble x，double y）;
double fs_exp（double x）;
double fs_log（double x）;
double fs_sqrt（double x ）;
#endif
/ * END fs_pow.h * /
/ * BEGIN fs_pow.c * /
#include< float.h>
#include" fs_pow.h"
double fs_pow（double x，double y）
{
double p;
if （0 x&& fs_fmod（y，1）== 0）{
if（fs_fmod（y，2）== 0）{
p = fs_exp（fs_log（-x）* y ）;
}其他{
p = -fs_exp（fs_log（-x）* y）;
}
} else {
if（x！= 0 || 0> = y）{
p = fs_exp（fs_log（x）* y）;
}否则{
p = 0;
}
}
返回p;
}
double fs_fmod（double x，double y）
{
double a，b;
const double c = x;
if（0 c）{
x = -x;
}
if（0 y）{
y = -y;
}
if（y！= 0&& DBL_MAX> = y&& DBL_MAX> = x）{
而（x> = y）{
a = x / 2 ;
b = y;
while（a> = b）{
b * = 2;
}
x - = b;
}
}否则{
x = 0;
}
返回0 c？ -x：x;
}
double fs_exp（double x）
{
unsigned n，square;
double b，e;
静态双x_max，x_min;
static int initialized;
if（！initialized）{
initialized = 1;
x_max = fs_log（DBL_MAX）;
x_min = fs_log（ DBL_MIN）;
}
if（x_max> = x&& x> = x_min）{
for（square = 0; x 1; x / = 2）{
++ square;
}
while（-1 x）{
++ square;
x / = 2;
}
e = b = n = 1;
做{
b / = n ++;
b * = x;
e + = b;
b / = n ++;
b * = x;
e + = b;
} while（b DBL_EPSILON / 4）;
while（square--！= 0）{
e * = e;
}
} else {
e = x 0？ DBL_MAX：0;
}
返回e;
}
double fs_log（double x ）
{
int n;
加倍a，b，c，epsilon;
静态双A， B，C;
static int initialized;
if（x 0&& LDBL_MAX> = x）{
if（！initialized）{
initialized = 1;
A = fs_sqrt（2）;
B = A / 2;
C = fs_log（A）;
}
for（n = 0; x A; x / = 2）{
++ n;
}
而（B x）{
--n;
x * = 2;
}
a =（x - 1）/（x + 1）;
x = C * n + a;
c = a * a;
n = 1;
epsilon = DBL_EPSILON * x;
if（0 a） {
if（epsilon 0）{
epsilon = -epsilon;
}
do {
n + = 2;
a * = c;
b = a / n;
x + = b;
} while（epsilon b）;
} else {
if（0 epsilon）{
epsilon = -epsilon;
}
做{
n + = 2;
a * = c;
b = a / n;
x + = b;
}而（b epsilon）;
}
x * = 2;
}否则{
x = -DBL_MAX;
}
返回x;
}
double fs_sqrt（double x）
{
int n;
加倍a，b;
if（x 0&& DBL_MAX> = x）{
for（n = 0; x 2; x / = 4）{
++ n;
}
while（0.5 x）{
--n;
x * = 4;
}
a = x;
b =（1 + x）/ 2;
do {
x = b;
b =（a / b + b）/ 2;
} while（xb）;
while（n 0）{
x * = 2;
- n;
}
而（0 n）{
x / = 2;
++ n;
}
}否则{
if（x！= 0） {
x = DBL_MAX;
}
}
返回x;
}
/ * END fs_pow.c * /
-
pete
/* BEGIN fs_pow_test.c */
#include <stdio.h>
/*
** fs_pow is implemented in portable freestanding code
*/
#include "fs_pow.h"
int main(void)
{
puts("/* BEGIN fs_pow_test.c output */\n");
printf("fs_pow(2, 4) is %f\n\n",
fs_pow(2, 4));
printf("fs_pow(0.0001, -0.25) - 10 is %e\n\n",
fs_pow(0.0001, -0.25) - 10);
puts("/* END fs_pow_test.c output */");
return 0;
}
/* END fs_pow_test.c */
/* BEGIN fs_pow.h */
/*
** Portable code for either freestanding or hosted
** implementations of C.
*/
#ifndef H_FS_POW_H
#define H_FS_POW_H
double fs_pow(double x, double y);
double fs_fmod(double x, double y);
double fs_exp(double x);
double fs_log(double x);
double fs_sqrt(double x);
#endif
/* END fs_pow.h */
/* BEGIN fs_pow.c */
#include <float.h>
#include "fs_pow.h"
double fs_pow(double x, double y)
{
double p;
if (0 x && fs_fmod(y, 1) == 0) {
if (fs_fmod(y, 2) == 0) {
p = fs_exp(fs_log(-x) * y);
} else {
p = -fs_exp(fs_log(-x) * y);
}
} else {
if (x != 0 || 0 >= y) {
p = fs_exp(fs_log( x) * y);
} else {
p = 0;
}
}
return p;
}
double fs_fmod(double x, double y)
{
double a, b;
const double c = x;
if (0 c) {
x = -x;
}
if (0 y) {
y = -y;
}
if (y != 0 && DBL_MAX >= y && DBL_MAX >= x) {
while (x >= y) {
a = x / 2;
b = y;
while (a >= b) {
b *= 2;
}
x -= b;
}
} else {
x = 0;
}
return 0 c ? -x : x;
}
double fs_exp(double x)
{
unsigned n, square;
double b, e;
static double x_max, x_min;
static int initialized;
if (!initialized) {
initialized = 1;
x_max = fs_log(DBL_MAX);
x_min = fs_log(DBL_MIN);
}
if (x_max >= x && x >= x_min) {
for (square = 0; x 1; x /= 2) {
++square;
}
while (-1 x) {
++square;
x /= 2;
}
e = b = n = 1;
do {
b /= n++;
b *= x;
e += b;
b /= n++;
b *= x;
e += b;
} while (b DBL_EPSILON / 4);
while (square-- != 0) {
e *= e;
}
} else {
e = x 0 ? DBL_MAX : 0;
}
return e;
}
double fs_log(double x)
{
int n;
double a, b, c, epsilon;
static double A, B, C;
static int initialized;
if (x 0 && LDBL_MAX >= x) {
if (!initialized) {
initialized = 1;
A = fs_sqrt(2);
B = A / 2;
C = fs_log(A);
}
for (n = 0; x A; x /= 2) {
++n;
}
while (B x) {
--n;
x *= 2;
}
a = (x - 1) / (x + 1);
x = C * n + a;
c = a * a;
n = 1;
epsilon = DBL_EPSILON * x;
if (0 a) {
if (epsilon 0) {
epsilon = -epsilon;
}
do {
n += 2;
a *= c;
b = a / n;
x += b;
} while (epsilon b);
} else {
if (0 epsilon) {
epsilon = -epsilon;
}
do {
n += 2;
a *= c;
b = a / n;
x += b;
} while (b epsilon);
}
x *= 2;
} else {
x = -DBL_MAX;
}
return x;
}
double fs_sqrt(double x)
{
int n;
double a, b;
if (x 0 && DBL_MAX >= x) {
for (n = 0; x 2; x /= 4) {
++n;
}
while (0.5 x) {
--n;
x *= 4;
}
a = x;
b = (1 + x) / 2;
do {
x = b;
b = (a / b + b) / 2;
} while (x b);
while (n 0) {
x *= 2;
--n;
}
while (0 n) {
x /= 2;
++n;
}
} else {
if (x != 0) {
x = DBL_MAX;
}
}
return x;
}
/* END fs_pow.c */
--
pete
pete写道：
pete wrote:
>
/ * BEGIN fs_pow.h * /
/ *
**独立或托管的便携代码
**实施C.
* /
#ifndef H_FS_POW_H
#define H_FS_POW_H
double fs_pow（double x，双y）;
double fs_fmod（double x，double y）;
double fs_exp（double x）;
double fs_log（double x ）;
double fs_sqrt（double x）;
>
/* BEGIN fs_pow.h */
/*
** Portable code for either freestanding or hosted
** implementations of C.
*/
#ifndef H_FS_POW_H
#define H_FS_POW_H
double fs_pow(double x, double y);
double fs_fmod(double x, double y);
double fs_exp(double x);
double fs_log(double x);
double fs_sqrt(double x);
有趣。代码的许可要求是什么？
-
Thad
Interesting. What are the license requirements on the code?
--
Thad
这篇关于替换'pow（）'功能的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
