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Code Issues Releases 1 Activity

added separate function for executing match copy command

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This commit is contained in:
Paul Cruz 2017-08-14 15:06:03 -07:00
parent d3e57db0bd
commit 9d56c21279
1 changed files with 44 additions and 34 deletions
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78
doc/educational_decoder/zstd_decompress.c
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@ -358,6 +358,10 @@ static u32 copy_literals(sequence_command_t seq, istream_t *litstream,
static size_t compute_offset(sequence_command_t seq, u64 *const offset_hist);
static void execute_match_copy(frame_context_t *const ctx, size_t offset,
size_t match_length, size_t total_output,
ostream_t *const out);
/******* END ZSTD HELPER STRUCTS AND PROTOTYPES *******************************/
size_t ZSTD_decompress(void *const dst, const size_t dst_len,
@ -1269,41 +1273,9 @@ static void execute_sequences(frame_context_t *const ctx, ostream_t *const out,
size_t match_length = seq.match_length;
u8 *write_ptr = IO_write_bytes(out, match_length);
if (total_output <= ctx->header.window_size) {
// In this case offset might go back into the dictionary
if (offset > total_output + ctx->dict_content_len) {
// The offset goes beyond even the dictionary
CORRUPTION();
}
execute_match_copy(ctx, offset, match_length, total_output, out);
if (offset > total_output) {
// "The rest of the dictionary is its content. The content act
// as a "past" in front of data to compress or decompress, so it
// can be referenced in sequence commands."
const size_t dict_copy =
MIN(offset - total_output, match_length);
const size_t dict_offset =
ctx->dict_content_len - (offset - total_output);
memcpy(write_ptr, ctx->dict_content + dict_offset, dict_copy);
write_ptr += dict_copy;
match_length -= dict_copy;
}
} else if (offset > ctx->header.window_size) {
CORRUPTION();
}
// We must copy byte by byte because the match length might be larger
// than the offset
// ex: if the output so far was "abc", a command with offset=3 and
// match_length=6 would produce "abcabcabc" as the new output
for (size_t j = 0; j < match_length; j++) {
*write_ptr = *(write_ptr - offset);
write_ptr++;
}
total_output += seq.match_length;
total_output += match_length;
}
// Copy any leftover literals
@ -1383,6 +1355,44 @@ static size_t compute_offset(sequence_command_t seq, u64 *const offset_hist) {
}
return offset;
}
static void execute_match_copy(frame_context_t *const ctx, size_t offset,
size_t match_length, size_t total_output,
ostream_t *const out) {
u8 *write_ptr = IO_write_bytes(out, match_length);
if (total_output <= ctx->header.window_size) {
// In this case offset might go back into the dictionary
if (offset > total_output + ctx->dict_content_len) {
// The offset goes beyond even the dictionary
CORRUPTION();
}
if (offset > total_output) {
// "The rest of the dictionary is its content. The content act
// as a "past" in front of data to compress or decompress, so it
// can be referenced in sequence commands."
const size_t dict_copy =
MIN(offset - total_output, match_length);
const size_t dict_offset =
ctx->dict_content_len - (offset - total_output);
memcpy(write_ptr, ctx->dict_content + dict_offset, dict_copy);
write_ptr += dict_copy;
match_length -= dict_copy;
}
} else if (offset > ctx->header.window_size) {
CORRUPTION();
}
// We must copy byte by byte because the match length might be larger
// than the offset
// ex: if the output so far was "abc", a command with offset=3 and
// match_length=6 would produce "abcabcabc" as the new output
for (size_t j = 0; j < match_length; j++) {
*write_ptr = *(write_ptr - offset);
write_ptr++;
}
}
/******* END SEQUENCE EXECUTION ***********************************************/
/******* OUTPUT SIZE COUNTING *************************************************/