[PATCH weston v2 12/21] Introduce a 'double fixed' data type abstraction
Jonas Ådahl
jadahl at gmail.com
Wed May 13 04:02:24 PDT 2015
On Wed, May 13, 2015 at 01:44:02PM +0300, Giulio Camuffo wrote:
> 2015-05-13 13:26 GMT+03:00 Jonas Ådahl <jadahl at gmail.com>:
> > The 'double fixed' value type is a fixed point data type implemented as
> > two signed 32 bit integers. It is intended to be sent over the wire and
> > used when wl_fixed_t is not detailed enough.
> >
> > Two helper functions are introduced: wl_double_fixed_to_double and
> > wl_double_fixed_from_double that can be used for conversion.
> >
> > The type is implemented by separating the integral part from the
> > fractional part, storing them in individual signed 32 bit integers.
> >
> > Converting to a double could be implemented with:
> >
> > double = integral + fraction / 2147483648
> >
> > Converting to a double could be implemented with:
> >
> > integral = integral part of double
> > fraction = fractional part of double * 2147483648
> >
> > The implementation provided in this patch is slightly faster than the
> > above methods, but assumes that the IEEE 754 double-precision binary
> > floating-point format is used internally. It is based on the wl_fixed_t
> > conversion functions from wayland-util.h.
> >
> > Signed-off-by: Jonas Ådahl <jadahl at gmail.com>
> > ---
> > Makefile.am | 6 +++
> > shared/util.h | 57 +++++++++++++++++++++
> > tests/double-fixed-benchmark.c | 110 +++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 173 insertions(+)
> > create mode 100644 shared/util.h
> > create mode 100644 tests/double-fixed-benchmark.c
> >
> > diff --git a/Makefile.am b/Makefile.am
> > index 2f16fac..0a30cb4 100644
> > --- a/Makefile.am
> > +++ b/Makefile.am
> > @@ -990,6 +990,7 @@ noinst_PROGRAMS += \
> > $(shared_tests) \
> > $(weston_tests) \
> > $(ivi_tests) \
> > + double-fixed-benchmark \
> > matrix-test
> >
> > test_module_ldflags = \
> > @@ -1102,6 +1103,11 @@ matrix_test_SOURCES = \
> > matrix_test_CPPFLAGS = -DUNIT_TEST
> > matrix_test_LDADD = -lm -lrt
> >
> > +double_fixed_benchmark_SOURCES = \
> > + tests/double-fixed-benchmark.c \
> > + shared/util.h
> > +double_fixed_benchmark_LDADD = -lm
> > +
> > if ENABLE_IVI_SHELL
> > module_tests += \
> > ivi-layout-internal-test.la \
> > diff --git a/shared/util.h b/shared/util.h
> > new file mode 100644
> > index 0000000..97a6f9b
> > --- /dev/null
> > +++ b/shared/util.h
> > @@ -0,0 +1,57 @@
> > +/*
> > + * Copyright © 2008 Kristian Høgsberg
> > + * Copyright © 2015 Red Hat Inc.
> > + *
> > + * Permission to use, copy, modify, distribute, and sell this software and its
> > + * documentation for any purpose is hereby granted without fee, provided that
> > + * the above copyright notice appear in all copies and that both that copyright
> > + * notice and this permission notice appear in supporting documentation, and
> > + * that the name of the copyright holders not be used in advertising or
> > + * publicity pertaining to distribution of the software without specific,
> > + * written prior permission. The copyright holders make no representations
> > + * about the suitability of this software for any purpose. It is provided "as
> > + * is" without express or implied warranty.
> > + *
> > + * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
> > + * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
> > + * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, 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.
> > + */
> > +
> > +#ifndef WESTON_SHARED_UTIL_H
> > +#define WESTON_SHARED_UTIL_H
> > +
> > +#include <math.h>
> > +
> > +static inline double
> > +wl_double_fixed_to_double(int32_t i, int32_t f)
>
> Should we have a struct wl_fixed_double_t { int32 i, int32 t } instead
> of having the two ints separated?
That is something I considered, since the wire format would still be ii,
the the dispatcher would still spit out int32_t i, int32_t f, we'd still
need to first put the ints in the struct, then convert the struct to a
double, so didn't seem like a big win. We could probably make the
sending side abstract the data type behind a struct though, but it'd be
a bit wierd to have the sender send a struct, and the receiver receive
two ints.
If we expect to keep a 64-bit fixed point around and not always convert
it to a double, then maybe it'd be worth it though. I'm probably easily
convinced to make that abstraction, if there are reasons enough to do
so.
Jonas
>
> > +{
> > + union {
> > + double d;
> > + int64_t i;
> > + } u;
> > +
> > + u.i = ((1023LL + (52LL - 31LL)) << 52) + (1LL << 51) + f;
> > +
> > + return i + (u.d - (3LL << (52 - 32)));
> > +}
> > +
> > +static inline void
> > +wl_double_fixed_from_double(double d, int32_t *i, int32_t *f)
> > +{
> > + double integral;
> > + union {
> > + double d;
> > + int64_t i;
> > + } u;
> > +
> > + u.d = modf(d, &integral) + (3LL << (51 - 31));
> > +
> > + *i = integral;
> > + *f = u.i;
> > +}
> > +
> > +#endif /* WESTON_SHARED_UTIL_H */
> > diff --git a/tests/double-fixed-benchmark.c b/tests/double-fixed-benchmark.c
> > new file mode 100644
> > index 0000000..e4e5685
> > --- /dev/null
> > +++ b/tests/double-fixed-benchmark.c
> > @@ -0,0 +1,110 @@
> > +/*
> > + * Copyright © 2012 Intel Corporation
> > + * Copyright © 2015 Red Hat Inc.
> > + *
> > + * Permission to use, copy, modify, distribute, and sell this software and its
> > + * documentation for any purpose is hereby granted without fee, provided that
> > + * the above copyright notice appear in all copies and that both that copyright
> > + * notice and this permission notice appear in supporting documentation, and
> > + * that the name of the copyright holders not be used in advertising or
> > + * publicity pertaining to distribution of the software without specific,
> > + * written prior permission. The copyright holders make no representations
> > + * about the suitability of this software for any purpose. It is provided "as
> > + * is" without express or implied warranty.
> > + *
> > + * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
> > + * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
> > + * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, 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.
> > + */
> > +
> > +#include <stdlib.h>
> > +#include <stdio.h>
> > +#include <string.h>
> > +#include <time.h>
> > +#include <assert.h>
> > +#include <stdint.h>
> > +#include "shared/util.h"
> > +
> > +volatile double global_d;
> > +
> > +static void
> > +noop_conversion(void)
> > +{
> > + int32_t fp;
> > +
> > + union {
> > + int64_t i;
> > + double d;
> > + } u;
> > +
> > + for (fp = 0; fp < INT32_MAX; fp++) {
> > + u.i = fp;
> > + global_d = u.d;
> > + }
> > +}
> > +
> > +static void
> > +magic_conversion(void)
> > +{
> > + int32_t fp;
> > +
> > + for (fp = 0; fp < INT32_MAX; fp++) {
> > + global_d = wl_double_fixed_to_double(fp, fp);
> > + }
> > +}
> > +
> > +static void
> > +mul_conversion(void)
> > +{
> > + int32_t fp;
> > +
> > + for (fp = 0; fp < INT32_MAX; fp++) {
> > + global_d = fp + fp / 2147483648.0;
> > + }
> > +}
> > +
> > +double factor = 2147483648.0;
> > +
> > +static void
> > +div_conversion(void)
> > +{
> > + int32_t fp;
> > +
> > + for (fp = 0; fp < INT32_MAX; fp++) {
> > + global_d = fp + fp / factor;
> > + }
> > +}
> > +
> > +static void
> > +benchmark(const char *s, void (*f)(void))
> > +{
> > + struct timespec start, stop, elapsed;
> > +
> > + clock_gettime(CLOCK_MONOTONIC, &start);
> > + f();
> > + clock_gettime(CLOCK_MONOTONIC, &stop);
> > +
> > + elapsed.tv_sec = stop.tv_sec - start.tv_sec;
> > + elapsed.tv_nsec = stop.tv_nsec - start.tv_nsec;
> > + if (elapsed.tv_nsec < 0) {
> > + elapsed.tv_nsec += 1000000000;
> > + elapsed.tv_sec--;
> > + }
> > + printf("benchmarked %s:\t%ld.%09lds\n",
> > + s, elapsed.tv_sec, elapsed.tv_nsec);
> > +}
> > +
> > +int
> > +main(int argc, char *argv[])
> > +{
> > + benchmark("noop", noop_conversion);
> > + benchmark("magic", magic_conversion);
> > + benchmark("div", div_conversion);
> > + benchmark("mul", mul_conversion);
> > +
> > + return 0;
> > +}
> > --
> > 2.1.4
> >
> > _______________________________________________
> > wayland-devel mailing list
> > wayland-devel at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/wayland-devel
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