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Add generic HAVE_RM_CTX implementation

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This patch adds a generic implementation of HAVE_RM_CTX using standard
fenv calls. As a result math functions using SET_RESTORE_ROUND* macros
do not suffer from a large slowdown on targets which do not implement
optimized libc_fe*_ctx inline functions. Most of the libc_fe* inline
functions are now unused and could be removed in the future (there are
a few math functions left which use a mixture of standard fenv calls
and libc_fe* inline functions - they could be updated to use
SET_RESTORE_ROUND or improved to avoid expensive fenv manipulations
across just a few FP instructions).

libc_feholdsetround*_noex_ctx is added to enable better optimization of
SET_RESTORE_ROUND_NOEX* implementations.

Performance measurements on ARM and x86 of sin() show significant gains
over the current default, fairly close to a highly optimized fenv_private:

                        ARM   x86
no fenv_private      : 100%  100%
generic HAVE_RM_CTX  : 250%  350%
fenv_private (CTX)   : 250%  450%

2014-06-23  Will Newton  <will.newton@linaro.org>
	    Wilco  <wdijkstr@arm.com>

	* sysdeps/generic/math_private.h: Add generic HAVE_RM_CTX
	implementation.  Include get-rounding-mode.h.
	[!HAVE_RM_CTX]: Define HAVE_RM_CTX to zero.
	[!libc_feholdsetround_noex_ctx]: Define
	libc_feholdsetround_noex_ctx.
	[!libc_feholdsetround_noexf_ctx]: Define
	libc_feholdsetround_noexf_ctx.
	[!libc_feholdsetround_noexl_ctx]: Define
	libc_feholdsetround_noexl_ctx.
	(libc_feholdsetround_ctx): New function.
	(libc_feresetround_ctx): New function.
	(libc_feholdsetround_noex_ctx): New function.
	(libc_feresetround_noex_ctx): New function.
This commit is contained in:
Wilco Dijkstra 2014-06-23 17:15:41 +01:00 committed by Will Newton
parent 88a4647493
commit e6d90d675d
2 changed files with 114 additions and 20 deletions
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17
ChangeLog
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@ -1,3 +1,20 @@
2014-06-23 Will Newton <will.newton@linaro.org>
Wilco <wdijkstr@arm.com>
* sysdeps/generic/math_private.h: Add generic HAVE_RM_CTX
implementation. Include get-rounding-mode.h.
[!HAVE_RM_CTX]: Define HAVE_RM_CTX to zero.
[!libc_feholdsetround_noex_ctx]: Define
libc_feholdsetround_noex_ctx.
[!libc_feholdsetround_noexf_ctx]: Define
libc_feholdsetround_noexf_ctx.
[!libc_feholdsetround_noexl_ctx]: Define
libc_feholdsetround_noexl_ctx.
(libc_feholdsetround_ctx): New function.
(libc_feresetround_ctx): New function.
(libc_feholdsetround_noex_ctx): New function.
(libc_feresetround_noex_ctx): New function.
2014-06-23 Roland McGrath <roland@hack.frob.com>
* sysdeps/unix/sysv/linux/mips/nptl/bits/pthreadtypes.h: Moved ...

117
sysdeps/generic/math_private.h
View File

@ -20,6 +20,7 @@
#include <stdint.h>
#include <sys/types.h>
#include <fenv.h>
#include <get-rounding-mode.h>
/* The original fdlibm code used statements like:
n0 = ((*(int*)&one)>>29)^1; * index of high word *
@ -551,12 +552,26 @@ default_libc_feupdateenv_test (fenv_t *e, int ex)
# define libc_feresetround_noexl libc_fesetenvl
#endif
#ifndef HAVE_RM_CTX
# define HAVE_RM_CTX 0
#endif
#if HAVE_RM_CTX
/* Set/Restore Rounding Modes only when necessary. If defined, these functions
set/restore floating point state only if the state needed within the lexical
block is different from the current state. This saves a lot of time when
the floating point unit is much slower than the fixed point units. */
# ifndef libc_feholdsetround_noex_ctx
# define libc_feholdsetround_noex_ctx libc_feholdsetround_ctx
# endif
# ifndef libc_feholdsetround_noexf_ctx
# define libc_feholdsetround_noexf_ctx libc_feholdsetroundf_ctx
# endif
# ifndef libc_feholdsetround_noexl_ctx
# define libc_feholdsetround_noexl_ctx libc_feholdsetroundl_ctx
# endif
# ifndef libc_feresetround_noex_ctx
# define libc_feresetround_noex_ctx libc_fesetenv_ctx
# endif
@ -567,24 +582,80 @@ default_libc_feupdateenv_test (fenv_t *e, int ex)
# define libc_feresetround_noexl_ctx libc_fesetenvl_ctx
# endif
# ifndef libc_feholdsetround_53bit_ctx
# define libc_feholdsetround_53bit_ctx libc_feholdsetround_ctx
# endif
# ifndef libc_feresetround_53bit_ctx
# define libc_feresetround_53bit_ctx libc_feresetround_ctx
# endif
# define SET_RESTORE_ROUND_GENERIC(RM,ROUNDFUNC,CLEANUPFUNC) \
struct rm_ctx ctx __attribute__((cleanup(CLEANUPFUNC ## _ctx))); \
ROUNDFUNC ## _ctx (&ctx, (RM))
#else
# define SET_RESTORE_ROUND_GENERIC(RM, ROUNDFUNC, CLEANUPFUNC) \
fenv_t __libc_save_rm __attribute__((cleanup(CLEANUPFUNC))); \
ROUNDFUNC (&__libc_save_rm, (RM))
/* Default implementation using standard fenv functions.
Avoid unnecessary rounding mode changes by first checking the
current rounding mode. Note the use of __glibc_unlikely is
important for performance. */
static __always_inline void
libc_feholdsetround_ctx (struct rm_ctx *ctx, int round)
{
ctx->updated_status = false;
/* Update rounding mode only if different. */
if (__glibc_unlikely (round != get_rounding_mode ()))
{
ctx->updated_status = true;
fegetenv (&ctx->env);
fesetround (round);
}
}
static __always_inline void
libc_feresetround_ctx (struct rm_ctx *ctx)
{
/* Restore the rounding mode if updated. */
if (__glibc_unlikely (ctx->updated_status))
feupdateenv (&ctx->env);
}
static __always_inline void
libc_feholdsetround_noex_ctx (struct rm_ctx *ctx, int round)
{
/* Save exception flags and rounding mode. */
fegetenv (&ctx->env);
/* Update rounding mode only if different. */
if (__glibc_unlikely (round != get_rounding_mode ()))
fesetround (round);
}
static __always_inline void
libc_feresetround_noex_ctx (struct rm_ctx *ctx)
{
/* Restore exception flags and rounding mode. */
fesetenv (&ctx->env);
}
# define libc_feholdsetroundf_ctx libc_feholdsetround_ctx
# define libc_feholdsetroundl_ctx libc_feholdsetround_ctx
# define libc_feresetroundf_ctx libc_feresetround_ctx
# define libc_feresetroundl_ctx libc_feresetround_ctx
# define libc_feholdsetround_noexf_ctx libc_feholdsetround_noex_ctx
# define libc_feholdsetround_noexl_ctx libc_feholdsetround_noex_ctx
# define libc_feresetround_noexf_ctx libc_feresetround_noex_ctx
# define libc_feresetround_noexl_ctx libc_feresetround_noex_ctx
#endif
/* Save and restore the rounding mode within a lexical block. */
#ifndef libc_feholdsetround_53bit_ctx
# define libc_feholdsetround_53bit_ctx libc_feholdsetround_ctx
#endif
#ifndef libc_feresetround_53bit_ctx
# define libc_feresetround_53bit_ctx libc_feresetround_ctx
#endif
#define SET_RESTORE_ROUND_GENERIC(RM,ROUNDFUNC,CLEANUPFUNC) \
struct rm_ctx ctx __attribute__((cleanup (CLEANUPFUNC ## _ctx))); \
ROUNDFUNC ## _ctx (&ctx, (RM))
/* Set the rounding mode within a lexical block. Restore the rounding mode to
the value at the start of the block. The exception mode must be preserved.
Exceptions raised within the block must be set in the exception flags.
Non-stop mode may be enabled inside the block. */
#define SET_RESTORE_ROUND(RM) \
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround, libc_feresetround)
@ -593,15 +664,21 @@ default_libc_feupdateenv_test (fenv_t *e, int ex)
#define SET_RESTORE_ROUNDL(RM) \
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetroundl, libc_feresetroundl)
/* Save and restore the rounding mode within a lexical block, and also
the set of exceptions raised within the block may be discarded. */
/* Set the rounding mode within a lexical block. Restore the rounding mode to
the value at the start of the block. The exception mode must be preserved.
Exceptions raised within the block must be discarded, and exception flags
are restored to the value at the start of the block.
Non-stop mode may be enabled inside the block. */
#define SET_RESTORE_ROUND_NOEX(RM) \
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround, libc_feresetround_noex)
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround_noex, \
libc_feresetround_noex)
#define SET_RESTORE_ROUND_NOEXF(RM) \
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetroundf, libc_feresetround_noexf)
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround_noexf, \
libc_feresetround_noexf)
#define SET_RESTORE_ROUND_NOEXL(RM) \
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetroundl, libc_feresetround_noexl)
SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround_noexl, \
libc_feresetround_noexl)
/* Like SET_RESTORE_ROUND, but also set rounding precision to 53 bits. */
#define SET_RESTORE_ROUND_53BIT(RM) \