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69a2d426f0
Since the delta data format is not tied to any actual git object anymore, now is the time to add a small improvement to the delta data header as it is been done for packed object header. This patch allows for reducing the delta header of about 2 bytes and makes for simpler code. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
95 lines
2.5 KiB
C
95 lines
2.5 KiB
C
/*
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* Copyright (C) 2005 Junio C Hamano
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* The delta-parsing part is almost straight copy of patch-delta.c
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* which is (C) 2005 Nicolas Pitre <nico@cam.org>.
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*/
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#include <stdlib.h>
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#include <string.h>
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#include <limits.h>
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#include "count-delta.h"
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static unsigned long get_hdr_size(const unsigned char **datap)
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{
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const unsigned char *data = *datap;
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unsigned char cmd = *data++;
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unsigned long size = cmd & ~0x80;
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int i = 7;
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while (cmd & 0x80) {
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cmd = *data++;
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size |= (cmd & ~0x80) << i;
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i += 7;
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}
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*datap = data;
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return size;
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}
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/*
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* NOTE. We do not _interpret_ delta fully. As an approximation, we
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* just count the number of bytes that are copied from the source, and
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* the number of literal data bytes that are inserted.
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*
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* Number of bytes that are _not_ copied from the source is deletion,
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* and number of inserted literal bytes are addition, so sum of them
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* is the extent of damage. xdelta can express an edit that copies
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* data inside of the destination which originally came from the
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* source. We do not count that in the following routine, so we are
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* undercounting the source material that remains in the final output
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* that way.
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*/
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int count_delta(void *delta_buf, unsigned long delta_size,
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unsigned long *src_copied, unsigned long *literal_added)
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{
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unsigned long copied_from_source, added_literal;
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const unsigned char *data, *top;
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unsigned char cmd;
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unsigned long src_size, dst_size, out;
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/* the smallest delta size possible is 4 bytes */
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if (delta_size < 4)
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return -1;
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data = delta_buf;
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top = delta_buf + delta_size;
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src_size = get_hdr_size(&data);
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dst_size = get_hdr_size(&data);
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added_literal = copied_from_source = out = 0;
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while (data < top) {
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cmd = *data++;
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if (cmd & 0x80) {
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unsigned long cp_off = 0, cp_size = 0;
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if (cmd & 0x01) cp_off = *data++;
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if (cmd & 0x02) cp_off |= (*data++ << 8);
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if (cmd & 0x04) cp_off |= (*data++ << 16);
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if (cmd & 0x08) cp_off |= (*data++ << 24);
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if (cmd & 0x10) cp_size = *data++;
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if (cmd & 0x20) cp_size |= (*data++ << 8);
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if (cp_size == 0) cp_size = 0x10000;
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if (cmd & 0x40)
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/* copy from dst */
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;
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else
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copied_from_source += cp_size;
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out += cp_size;
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} else {
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/* write literal into dst */
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added_literal += cmd;
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out += cmd;
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data += cmd;
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}
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}
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/* sanity check */
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if (data != top || out != dst_size)
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return -1;
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/* delete size is what was _not_ copied from source.
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* edit size is that and literal additions.
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*/
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*src_copied = copied_from_source;
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*literal_added = added_literal;
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return 0;
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}
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