Correct the overflow limit in the variable o_threshold to be consistent
with the FLT_UWORD_LOG_MAX variable used by the internal implementation
of the expf algorithm itself.
The u_threshold variable has also been modified to be written in the
same format.
Note that this fix improves the situation but does not completely
correct the inconsistencies regarding the overflow and underflow limits
between the expf wrapper (wf_exp.c) and the expf algorithm itself
(ef_exp.c).
Currently these limits are different for the
_FLT_LARGEST_EXPONENT_IS_NORMAL and _FLT_NO_DENORMALS cases as well as
for the case where __OBSOLETE_MATH is not defined (only for the
underflow limit in this case).
This patch removes the definitions of HUGE_VAL from some of the float math
functions. HUGE_VAL is defined in newlib/libc/include/math.h, so it is not
necessary to have a further definition in the math functions.
Based on code from https://github.com/ARM-software/optimized-routines/
This patch adds a highly optimized generic implementation of expf,
exp2f, logf, log2f and powf. The new functions are not only
faster (6x for powf!), but are also smaller and more accurate.
In order to achieve this, the algorithm uses double precision
arithmetic for accuracy, avoids divisions and uses small table
lookups to minimize the polynomials. Special cases are handled
inline to avoid the unnecessary overhead of wrapper functions and
set errno to POSIX requirements.
The new functions are added under newlib/libm/common, but the old
implementations are kept (in newlib/libm/math) for non-IEEE or
pre-C99 systems. Targets can enable the new math code by defining
__OBSOLETE_MATH_DEFAULT to 0 in newlib/libc/include/machine/ieeefp.h,
users can override the default by defining __OBSOLETE_MATH.
Currently the new code is enabled for AArch64 and AArch32 with VFP.
Targets with a single precision FPU may still prefer the old
implementation.
libm.a size changes:
arm: -1692
arm/thumb/v7-a/nofp: -878
arm/thumb/v7-a+fp/hard: -864
arm/thumb/v7-a+fp/softfp: -908
aarch64: -1476
Andoni Arregi
Jozef Lawrynowicz
Szabolcs Nagy
Christopher Faylor