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

libs/libc/math: Small change to log() and logf() that improves accuracy and convergence time

Browse Source
This commit is contained in:
Rajan Gill 2018-09-16 15:14:15 -06:00 committed by Gregory Nutt
parent ed5620897f
commit d647127d14
2 changed files with 22 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
libs/libc/math/lib_log.c
View File

@ -60,24 +60,24 @@ double log(double x)
{
double y;
double y_old;
double ey;
double ney;
double epsilon;
int relax_factor;
int i;
int iter;
y = 0.0;
y_old = 1.0;
epsilon = DBL_EPSILON;
i = 0;
iter = 0;
relax_factor = 1;
while (y > y_old + epsilon || y < y_old - epsilon)
{
y_old = y;
ey = exp(y);
y -= (ey - x) / ey;
ney = exp(-y);
y -= 1 - x * ney;
if (y > 700.0)
{
@ -91,13 +91,16 @@ double log(double x)
epsilon = (fabs(y) > 1.0) ? fabs(y) * DBL_EPSILON : DBL_EPSILON;
if (++i >= LOGF_MAX_ITER)
if (++iter >= LOGF_MAX_ITER)
{
relax_factor *= LOGF_RELAX_MULTIPLIER;
i = 0;
iter = 0;
}
epsilon *= relax_factor;
if (relax_factor > 1)
{
epsilon *= relax_factor;
}
}
if (y == 700.0)

19
libs/libc/math/lib_logf.c
View File

@ -58,23 +58,23 @@ float logf(float x)
{
float y;
float y_old;
float ey;
float ney;
float epsilon;
int relax_factor;
int i;
int iter;
y = 0.0F;
y_old = 1.0F;
epsilon = FLT_EPSILON;
i = 0;
iter = 0;
relax_factor = 1;
while (y > y_old + epsilon || y < y_old - epsilon)
{
y_old = y;
ey = expf(y);
y -= (ey - x) / ey;
ney = expf(-y);
y -= 1 - x * ney;
if (y > FLT_MAX_EXP_X)
{
@ -88,13 +88,16 @@ float logf(float x)
epsilon = (fabsf(y) > 1.0F) ? fabsf(y) * FLT_EPSILON : FLT_EPSILON;
if (++i >= LOGF_MAX_ITER)
if (++iter >= LOGF_MAX_ITER)
{
relax_factor *= LOGF_RELAX_MULTIPLIER;
i = 0;
iter = 0;
}
epsilon *= relax_factor;
if (relax_factor > 1)
{
epsilon *= relax_factor;
}
}
if (y == FLT_MAX_EXP_X)