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liblzma: Add comments.
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@ -474,6 +474,15 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
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// Variable number (1-5) of bits
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// Variable number (1-5) of bits
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// from a reverse bittree. This
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// from a reverse bittree. This
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// isn't worth manual unrolling.
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// isn't worth manual unrolling.
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//
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// NOTE: Making one or many of the
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// variables (probs, symbol, offset,
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// or limit) local here (instead of
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// using those declared outside the
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// main loop) can affect code size
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// and performance which isn't a
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// surprise but it's not so clear
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// what is the best.
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do {
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do {
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rc_bit_add_if_1(probs,
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rc_bit_add_if_1(probs,
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rep0, offset);
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rep0, offset);
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@ -305,8 +305,15 @@ do { \
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} while (0)
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} while (0)
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// Decode one bit from variable-sized reverse bittree.
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// Decode one bit from variable-sized reverse bittree. The loop is done
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// The loop is done in the code that uses this macro.
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// in the code that uses this macro. This could be changed if the assembly
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// version benefited from having the loop done in assembly but it didn't
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// seem so in early 2024.
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//
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// Also, if the loop was done here, the loop counter would likely be local
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// to the macro so that it wouldn't modify yet another input variable.
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// If a _safe version of a macro with a loop was done then a modifiable
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// input variable couldn't be avoided though.
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#define rc_bit_add_if_1(probs, dest, value_to_add_if_1) \
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#define rc_bit_add_if_1(probs, dest, value_to_add_if_1) \
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rc_bit(probs[symbol], \
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rc_bit(probs[symbol], \
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, \
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, \
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