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95 lines
2.5 KiB
95 lines
2.5 KiB
/* |
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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 long size; |
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unsigned char cmd; |
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int i; |
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size = i = 0; |
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cmd = *data++; |
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while (cmd) { |
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if (cmd & 1) |
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size |= *data++ << i; |
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i += 8; |
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cmd >>= 1; |
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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. Number of |
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* bytes that are _not_ copied from the source is deletion, and number |
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* of inserted literal bytes are addition, so sum of them is what we |
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* return. xdelta can express an edit that copies data inside of the |
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* destination which originally came from the source. We do not count |
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* that in the following routine, so we are undercounting the source |
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* material that remains in the final output that way. |
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*/ |
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unsigned long count_delta(void *delta_buf, unsigned long delta_size) |
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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 6 bytes */ |
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if (delta_size < 6) |
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return UINT_MAX; |
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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 UINT_MAX; |
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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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if (src_size + added_literal < copied_from_source) |
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/* we ended up overcounting and underflowed */ |
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return 0; |
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return (src_size - copied_from_source) + added_literal; |
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}
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