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libs/libc/math: Add variable convergence in log() and logf() to avoid hangs caused by failure to converge for very specific input values.

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This commit is contained in:
Rajan Gill 2018-09-16 12:22:36 -06:00 committed by Gregory Nutt
parent 9f8f1cc5cf
commit 6da2658fdd
2 changed files with 61 additions and 3 deletions
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37
libs/libc/math/lib_log.c
View File

@ -3,7 +3,7 @@
* *
* This file is a part of NuttX: * This file is a part of NuttX:
* *
* Copyright (C) 2012 Gregory Nutt. All rights reserved. * Copyright (C) 2012, 2018 Gregory Nutt. All rights reserved.
* Ported by: Darcy Gong * Ported by: Darcy Gong
* *
* It derives from the Rhombus OS math library by Nick Johnson which has * It derives from the Rhombus OS math library by Nick Johnson which has
@ -35,19 +35,44 @@
#include <math.h> #include <math.h>
#include <float.h> #include <float.h>
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* To avoid looping forever in particular corner cases, every LOGF_MAX_ITER
* the error criteria is relaxed by a factor LOGF_RELAX_MULTIPLIER.
* todo: might need to adjust the double floating point version too.
*/
#define LOGF_MAX_ITER 10
#define LOGF_RELAX_MULTIPLIER 2
/**************************************************************************** /****************************************************************************
* Public Functions * Public Functions
****************************************************************************/ ****************************************************************************/
/****************************************************************************
* Name: log
****************************************************************************/
#ifdef CONFIG_HAVE_DOUBLE #ifdef CONFIG_HAVE_DOUBLE
double log(double x) double log(double x)
{ {
double y, y_old, ey, epsilon; double y;
double y_old;
double ey;
double epsilon;
int relax_factor;
int i;
y = 0.0; y = 0.0;
y_old = 1.0; y_old = 1.0;
epsilon = DBL_EPSILON; epsilon = DBL_EPSILON;
i = 0;
relax_factor = 1;
while (y > y_old + epsilon || y < y_old - epsilon) while (y > y_old + epsilon || y < y_old - epsilon)
{ {
y_old = y; y_old = y;
@ -65,6 +90,14 @@ double log(double x)
} }
epsilon = (fabs(y) > 1.0) ? fabs(y) * DBL_EPSILON : DBL_EPSILON; epsilon = (fabs(y) > 1.0) ? fabs(y) * DBL_EPSILON : DBL_EPSILON;
if (++i >= LOGF_MAX_ITER)
{
relax_factor *= LOGF_RELAX_MULTIPLIER;
i = 0;
}
epsilon *= relax_factor;
} }
if (y == 700.0) if (y == 700.0)

27
libs/libc/math/lib_logf.c
View File

@ -3,7 +3,7 @@
* *
* This file is a part of NuttX: * This file is a part of NuttX:
* *
* Copyright (C) 2012, 2017 Gregory Nutt. All rights reserved. * Copyright (C) 2012, 2017-2018 Gregory Nutt. All rights reserved.
* Ported by: Darcy Gong * Ported by: Darcy Gong
* *
* It derives from the Rhombus OS math library by Nick Johnson which has * It derives from the Rhombus OS math library by Nick Johnson which has
@ -32,8 +32,20 @@
#include <math.h> #include <math.h>
#include <float.h> #include <float.h>
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#define FLT_MAX_EXP_X 88.0F #define FLT_MAX_EXP_X 88.0F
/* To avoid looping forever in particular corner cases, every LOGF_MAX_ITER
* the error criteria is relaxed by a factor LOGF_RELAX_MULTIPLIER.
* todo: might need to adjust the double floating point version too.
*/
#define LOGF_MAX_ITER 10
#define LOGF_RELAX_MULTIPLIER 2
/**************************************************************************** /****************************************************************************
* Public Functions * Public Functions
****************************************************************************/ ****************************************************************************/
@ -48,11 +60,16 @@ float logf(float x)
float y_old; float y_old;
float ey; float ey;
float epsilon; float epsilon;
int relax_factor;
int i;
y = 0.0F; y = 0.0F;
y_old = 1.0F; y_old = 1.0F;
epsilon = FLT_EPSILON; epsilon = FLT_EPSILON;
i = 0;
relax_factor = 1;
while (y > y_old + epsilon || y < y_old - epsilon) while (y > y_old + epsilon || y < y_old - epsilon)
{ {
y_old = y; y_old = y;
@ -70,6 +87,14 @@ float logf(float x)
} }
epsilon = (fabsf(y) > 1.0F) ? fabsf(y) * FLT_EPSILON : FLT_EPSILON; epsilon = (fabsf(y) > 1.0F) ? fabsf(y) * FLT_EPSILON : FLT_EPSILON;
if (++i >= LOGF_MAX_ITER)
{
relax_factor *= LOGF_RELAX_MULTIPLIER;
i = 0;
}
epsilon *= relax_factor;
} }
if (y == FLT_MAX_EXP_X) if (y == FLT_MAX_EXP_X)