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e7ad4a9c3c
There was a stale comment that explains why the old code could undercount when delta data copied things around inside detination buffer. We do not use that kind of delta, so the comment does not apply.
72 lines
1.9 KiB
C
72 lines
1.9 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 "delta.h"
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#include "count-delta.h"
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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.
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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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if (delta_size < DELTA_SIZE_MIN)
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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_delta_hdr_size(&data);
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dst_size = get_delta_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 (cmd & 0x40) cp_size |= (*data++ << 16);
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if (cp_size == 0) cp_size = 0x10000;
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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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