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authorLasse Collin <lasse.collin@tukaani.org>2022-09-20 16:58:22 +0300
committerLasse Collin <lasse.collin@tukaani.org>2022-09-20 16:58:22 +0300
commitf664cb25841fc1c478b819034a224a558e2ac6e7 (patch)
tree295536d6db51fb1eeb536670b875dcfb808850ce /src/liblzma/simple/arm64.c
parentliblzma: ARM64: Fix wrong comment in API doc. (diff)
downloadxz-f664cb25841fc1c478b819034a224a558e2ac6e7.tar.xz
liblzma: ARM64: Add comments.
Diffstat (limited to 'src/liblzma/simple/arm64.c')
-rw-r--r--src/liblzma/simple/arm64.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/src/liblzma/simple/arm64.c b/src/liblzma/simple/arm64.c
index 911e30c1..0437f736 100644
--- a/src/liblzma/simple/arm64.c
+++ b/src/liblzma/simple/arm64.c
@@ -72,6 +72,9 @@ arm64_code(void *simple_ptr, uint32_t now_pos, bool is_encoder,
src <<= 2;
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
&& (src & sign_mask) != sign_mask)
continue;
@@ -197,7 +200,17 @@ arm64_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,
lzma_simple_coder *coder = next->coder;
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);
+
+ // 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;
}