b859f2750b
Probably this is a bug of a GCC, but on AMRv7 the code "if (relax_factor > 1)" generates "bne.n" instruction if "relax_factor" is "int". Few lines above "relax_factor *= LOG_RELAX_MULTIPLIER;" is done without overflow check hence at some moment overflow occurs and "relax_factor" becomes a zero and condition "if (relax_factor > 1)" becomes always evaluated to "true" hence "epsilon" becomes zero always. Probably this is not the best way to fix the bug (The best way is to report it to GCC), but this change allows to get correct behavior of "log" and "logf" for ARMv7 based MCUs Signed-off-by: Petro Karashchenko <petro.karashchenko@gmail.com>
115 lines
3.2 KiB
C
115 lines
3.2 KiB
C
/****************************************************************************
|
|
* libs/libc/math/lib_logf.c
|
|
*
|
|
* This file is a part of NuttX:
|
|
*
|
|
* Copyright (C) 2012, 2017-2018 Gregory Nutt. All rights reserved.
|
|
* Ported by: Darcy Gong
|
|
*
|
|
* It derives from the Rhombus OS math library by Nick Johnson which has
|
|
* a compatibile, MIT-style license:
|
|
*
|
|
* Copyright (C) 2009, 2010 Nick Johnson <nickbjohnson4224 at gmail.com>
|
|
*
|
|
* Permission to use, copy, modify, and distribute this software for any
|
|
* purpose with or without fee is hereby granted, provided that the above
|
|
* copyright notice and this permission notice appear in all copies.
|
|
*
|
|
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
|
|
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
|
|
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
|
|
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
|
|
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
|
|
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
|
|
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
|
|
*
|
|
****************************************************************************/
|
|
|
|
/****************************************************************************
|
|
* Included Files
|
|
****************************************************************************/
|
|
|
|
#include <math.h>
|
|
#include <float.h>
|
|
|
|
/****************************************************************************
|
|
* Pre-processor Definitions
|
|
****************************************************************************/
|
|
|
|
#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 2.0F
|
|
|
|
/****************************************************************************
|
|
* Public Functions
|
|
****************************************************************************/
|
|
|
|
/****************************************************************************
|
|
* Name: logf
|
|
****************************************************************************/
|
|
|
|
float logf(float x)
|
|
{
|
|
float y;
|
|
float y_old;
|
|
float ey;
|
|
float epsilon;
|
|
float relax_factor;
|
|
int iter;
|
|
|
|
y = 0.0F;
|
|
y_old = 1.0F;
|
|
epsilon = FLT_EPSILON;
|
|
|
|
iter = 0;
|
|
relax_factor = 1.0F;
|
|
|
|
while (y > y_old + epsilon || y < y_old - epsilon)
|
|
{
|
|
y_old = y;
|
|
ey = expf(y);
|
|
y -= (ey - x) / ey;
|
|
|
|
if (y > FLT_MAX_EXP_X)
|
|
{
|
|
y = FLT_MAX_EXP_X;
|
|
}
|
|
|
|
if (y < -FLT_MAX_EXP_X)
|
|
{
|
|
y = -FLT_MAX_EXP_X;
|
|
}
|
|
|
|
epsilon = (fabsf(y) > 1.0F) ? fabsf(y) * FLT_EPSILON : FLT_EPSILON;
|
|
|
|
if (++iter >= LOGF_MAX_ITER)
|
|
{
|
|
relax_factor *= LOGF_RELAX_MULTIPLIER;
|
|
iter = 0;
|
|
}
|
|
|
|
if (relax_factor > 1.0F)
|
|
{
|
|
epsilon *= relax_factor;
|
|
}
|
|
}
|
|
|
|
if (y == FLT_MAX_EXP_X)
|
|
{
|
|
return INFINITY;
|
|
}
|
|
|
|
if (y == -FLT_MAX_EXP_X)
|
|
{
|
|
return INFINITY;
|
|
}
|
|
|
|
return y;
|
|
}
|