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6b5b3a27b7
Commit a201c20
tried to optimize out a loop like:
for (i = 0; i < len; i++)
data[i] = ntohll(data[i]);
in the big-endian case, because we know that ntohll is a
noop, and we do not need to pay the cost of the loop at all.
However, it mistakenly assumed that __BYTE_ORDER was always
defined, whereas it may not be on systems which do not
define it by default, and where we did not need to define it
to set up the ntohll macro. This includes OS X and Windows.
We could muck with the ordering in compat/bswap.h to make
sure it is defined unconditionally, but it is simpler to
still to just execute the loop unconditionally. That avoids
the application code knowing anything about these magic
macros, and lets it depend only on having ntohll defined.
And since the resulting loop looks like (on a big-endian
system):
for (i = 0; i < len; i++)
data[i] = data[i];
any decent compiler can probably optimize it out.
Original report and analysis by Brian Gernhardt.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
204 lines
5.2 KiB
C
204 lines
5.2 KiB
C
/**
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* Copyright 2013, GitHub, Inc
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* Copyright 2009-2013, Daniel Lemire, Cliff Moon,
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* David McIntosh, Robert Becho, Google Inc. and Veronika Zenz
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include "git-compat-util.h"
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#include "ewok.h"
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int ewah_serialize_native(struct ewah_bitmap *self, int fd)
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{
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uint32_t write32;
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size_t to_write = self->buffer_size * 8;
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/* 32 bit -- bit size for the map */
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write32 = (uint32_t)self->bit_size;
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if (write(fd, &write32, 4) != 4)
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return -1;
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/** 32 bit -- number of compressed 64-bit words */
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write32 = (uint32_t)self->buffer_size;
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if (write(fd, &write32, 4) != 4)
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return -1;
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if (write(fd, self->buffer, to_write) != to_write)
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return -1;
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/** 32 bit -- position for the RLW */
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write32 = self->rlw - self->buffer;
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if (write(fd, &write32, 4) != 4)
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return -1;
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return (3 * 4) + to_write;
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}
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int ewah_serialize_to(struct ewah_bitmap *self,
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int (*write_fun)(void *, const void *, size_t),
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void *data)
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{
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size_t i;
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eword_t dump[2048];
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const size_t words_per_dump = sizeof(dump) / sizeof(eword_t);
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uint32_t bitsize, word_count, rlw_pos;
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const eword_t *buffer;
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size_t words_left;
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/* 32 bit -- bit size for the map */
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bitsize = htonl((uint32_t)self->bit_size);
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if (write_fun(data, &bitsize, 4) != 4)
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return -1;
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/** 32 bit -- number of compressed 64-bit words */
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word_count = htonl((uint32_t)self->buffer_size);
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if (write_fun(data, &word_count, 4) != 4)
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return -1;
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/** 64 bit x N -- compressed words */
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buffer = self->buffer;
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words_left = self->buffer_size;
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while (words_left >= words_per_dump) {
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for (i = 0; i < words_per_dump; ++i, ++buffer)
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dump[i] = htonll(*buffer);
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if (write_fun(data, dump, sizeof(dump)) != sizeof(dump))
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return -1;
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words_left -= words_per_dump;
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}
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if (words_left) {
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for (i = 0; i < words_left; ++i, ++buffer)
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dump[i] = htonll(*buffer);
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if (write_fun(data, dump, words_left * 8) != words_left * 8)
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return -1;
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}
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/** 32 bit -- position for the RLW */
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rlw_pos = (uint8_t*)self->rlw - (uint8_t *)self->buffer;
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rlw_pos = htonl(rlw_pos / sizeof(eword_t));
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if (write_fun(data, &rlw_pos, 4) != 4)
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return -1;
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return (3 * 4) + (self->buffer_size * 8);
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}
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static int write_helper(void *fd, const void *buf, size_t len)
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{
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return write((intptr_t)fd, buf, len);
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}
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int ewah_serialize(struct ewah_bitmap *self, int fd)
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{
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return ewah_serialize_to(self, write_helper, (void *)(intptr_t)fd);
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}
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int ewah_read_mmap(struct ewah_bitmap *self, void *map, size_t len)
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{
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uint8_t *ptr = map;
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size_t i;
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self->bit_size = get_be32(ptr);
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ptr += sizeof(uint32_t);
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self->buffer_size = self->alloc_size = get_be32(ptr);
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ptr += sizeof(uint32_t);
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self->buffer = ewah_realloc(self->buffer,
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self->alloc_size * sizeof(eword_t));
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if (!self->buffer)
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return -1;
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/*
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* Copy the raw data for the bitmap as a whole chunk;
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* if we're in a little-endian platform, we'll perform
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* the endianness conversion in a separate pass to ensure
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* we're loading 8-byte aligned words.
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*/
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memcpy(self->buffer, ptr, self->buffer_size * sizeof(uint64_t));
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ptr += self->buffer_size * sizeof(uint64_t);
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for (i = 0; i < self->buffer_size; ++i)
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self->buffer[i] = ntohll(self->buffer[i]);
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self->rlw = self->buffer + get_be32(ptr);
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return (3 * 4) + (self->buffer_size * 8);
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}
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int ewah_deserialize(struct ewah_bitmap *self, int fd)
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{
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size_t i;
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eword_t dump[2048];
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const size_t words_per_dump = sizeof(dump) / sizeof(eword_t);
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uint32_t bitsize, word_count, rlw_pos;
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eword_t *buffer = NULL;
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size_t words_left;
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ewah_clear(self);
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/* 32 bit -- bit size for the map */
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if (read(fd, &bitsize, 4) != 4)
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return -1;
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self->bit_size = (size_t)ntohl(bitsize);
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/** 32 bit -- number of compressed 64-bit words */
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if (read(fd, &word_count, 4) != 4)
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return -1;
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self->buffer_size = self->alloc_size = (size_t)ntohl(word_count);
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self->buffer = ewah_realloc(self->buffer,
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self->alloc_size * sizeof(eword_t));
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if (!self->buffer)
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return -1;
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/** 64 bit x N -- compressed words */
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buffer = self->buffer;
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words_left = self->buffer_size;
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while (words_left >= words_per_dump) {
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if (read(fd, dump, sizeof(dump)) != sizeof(dump))
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return -1;
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for (i = 0; i < words_per_dump; ++i, ++buffer)
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*buffer = ntohll(dump[i]);
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words_left -= words_per_dump;
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}
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if (words_left) {
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if (read(fd, dump, words_left * 8) != words_left * 8)
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return -1;
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for (i = 0; i < words_left; ++i, ++buffer)
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*buffer = ntohll(dump[i]);
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}
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/** 32 bit -- position for the RLW */
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if (read(fd, &rlw_pos, 4) != 4)
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return -1;
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self->rlw = self->buffer + ntohl(rlw_pos);
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return 0;
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}
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