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liblzma: ARM64: Add comments.

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This commit is contained in:
Lasse Collin 2022-09-20 16:58:22 +03:00
parent b557b4a0ee
commit f664cb2584
1 changed files with 13 additions and 0 deletions
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13
src/liblzma/simple/arm64.c
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@ -72,6 +72,9 @@ arm64_code(void *simple_ptr, uint32_t now_pos, bool is_encoder,
src <<= 2; src <<= 2;
src &= ADDR28_MASK; src &= ADDR28_MASK;
// When the conversion width isn't the maximum,
// check that the highest bits are either all zero
// or all one.
if ((src & sign_mask) != 0 if ((src & sign_mask) != 0
&& (src & sign_mask) != sign_mask) && (src & sign_mask) != sign_mask)
continue; continue;
@ -197,7 +200,17 @@ arm64_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,
lzma_simple_coder *coder = next->coder; lzma_simple_coder *coder = next->coder;
lzma_simple_arm64 *simple = coder->simple; lzma_simple_arm64 *simple = coder->simple;
// This will be used to detect if the value, after
// conversion has been done, is negative. The location
// of the sign bit depends on the conversion width.
simple->sign_bit = UINT32_C(1) << (opt->width - 1); simple->sign_bit = UINT32_C(1) << (opt->width - 1);
// When conversion width isn't the maximum, the highest
// bits must all be either zero or one, that is, they
// all are copies of the sign bit. This mask is used to
// (1) detect if input value is in the range specified
// by the conversion width and (2) clearing or setting
// the high bits after conversion (integers can wrap around).
simple->sign_mask = (UINT32_C(1) << 28) - simple->sign_bit; simple->sign_mask = (UINT32_C(1) << 28) - simple->sign_bit;
} }