sergiotarxz/nuttx
sergiotarxz/nuttx
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

libs/libc/math: Fix calculation error of log function

Browse Source 
Fix a problem where the log function would loop infinitely by
calculation error when a specific value was passed. For example,
in the following case, the log function loops infinitely and
never returns. So, this commit fixes to return the right value.

  double a = 7883961.5;
  double b = log(a);
This commit is contained in:
SPRESENSE 2021-07-10 21:14:17 +09:00 committed by Xiang Xiao
parent 5fe51b923a
commit 2e80d5e38e
2 changed files with 6 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
libs/libc/math/lib_log.c
View File

@ -60,7 +60,7 @@ double log(double x)
{ {
double y; double y;
double y_old; double y_old;
double ney; double ey;
double epsilon; double epsilon;
int relax_factor; int relax_factor;
int iter; int iter;
@ -75,8 +75,8 @@ double log(double x)
while (y > y_old + epsilon || y < y_old - epsilon) while (y > y_old + epsilon || y < y_old - epsilon)
{ {
y_old = y; y_old = y;
ney = exp(-y); ey = exp(y);
y -= 1.0 - x * ney; y -= (ey - x) / ey;
if (y > 700.0) if (y > 700.0)
{ {

6
libs/libc/math/lib_logf.c
View File

@ -58,7 +58,7 @@ float logf(float x)
{ {
float y; float y;
float y_old; float y_old;
float ney; float ey;
float epsilon; float epsilon;
int relax_factor; int relax_factor;
int iter; int iter;
@ -73,8 +73,8 @@ float logf(float x)
while (y > y_old + epsilon || y < y_old - epsilon) while (y > y_old + epsilon || y < y_old - epsilon)
{ {
y_old = y; y_old = y;
ney = expf(-y); ey = expf(y);
y -= 1.0F - x * ney; y -= (ey - x) / ey;
if (y > FLT_MAX_EXP_X) if (y > FLT_MAX_EXP_X)
{ {