cvs commit: src/lib/msun/src e_lgammaf_r.c k_cosf.c k_sinf.c
math_private.h s_cosf.c s_sinf.c
Bruce Evans
bde at FreeBSD.org
Mon Nov 28 04:58:58 GMT 2005
bde 2005-11-28 04:58:57 UTC
FreeBSD src repository
Modified files:
lib/msun/src e_lgammaf_r.c k_cosf.c k_sinf.c
math_private.h s_cosf.c s_sinf.c
Log:
Use only double precision for "kernel" cosf and sinf (except for
returning float). The functions are renamed from __kernel_{cos,sin}f()
to __kernel_{cos,sin}df() so that misuses of them will cause link errors
and not crashes.
This version is an almost-routine translation with no special optimizations
for accuracy or efficiency. The not-quite-routine part is that in
__kernel_cosf(), regenerating the minimax polynomial with double
precision coefficients gives a coefficient for the x**2 term that is
not quite -0.5, so the literal 0.5 in the code and the related `hz'
variable need to be modified; also, the special code for reducing the
error in 1.0-x**2*0.5 is no longer needed, so it is convenient to
adjust all the logic for the x**2 term a little. Note that without
extra precision, it would be very bad to use a coefficient of other
than -0.5 for the x**2 term -- the old version depends on multiplication
by -0.5 being infinitely precise so as not to need even more special
code for reducing the error in 1-x**2*0.5.
This gives an unimportant increase in accuracy, from ~0.8 to ~0.501
ulps. Almost all of the error is from the final rounding step, since
the choice of the minimax polynomials so that their contribution to the
error is a bit less than 0.5 ulps just happens to give contributions that
are significantly less (~.001 ulps).
An Athlons, for uniformly distributed args in [-2pi, 2pi], this gives
overall speed increases in the 10-20% range, despite giving a speed
decrease of typically 19% (from 31 cycles up to 37) for sinf() on args
in [-pi/4, pi/4].
Revision Changes Path
1.8 +6 -6 src/lib/msun/src/e_lgammaf_r.c
1.14 +11 -12 src/lib/msun/src/k_cosf.c
1.12 +11 -13 src/lib/msun/src/k_sinf.c
1.20 +2 -2 src/lib/msun/src/math_private.h
1.12 +7 -19 src/lib/msun/src/s_cosf.c
1.12 +7 -19 src/lib/msun/src/s_sinf.c
More information about the cvs-src
mailing list