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swscale/aarch64: fix uyvy/yuyv to yuv420p/yuv422p on odd width

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interleaved_yuv_to_planar, shared by uyvytoyuv422, uyvytoyuv420,
yuyvtoyuv422 and yuyvtoyuv420, only handled even widths. The packed
UYVY/YUYV macroblocks are pixel pairs and the trailing half macroblock of
an odd width was mishandled:

- the slow path (width <= 31) decrements its pixel counter by two from an
  odd value, so it never reaches zero and the loop runs far past the line,
  overwriting the destination (observed as a crash in checkasm);
- the fast path (width >= 32) shifts the tail pointers back by width-32 and
  reprocesses an overlapping, misaligned tuple, producing wrong samples and
  dropping the last chroma column.

Process only whole pixel pairs and emit the trailing odd column from a
per-line epilogue that matches the C reference: for yuv422 one Y, U and V
sample; for yuv420 the Y of both lines of the pair with the chroma averaged
across them, and luma only for the final line when the height is odd. The
empty even part (width 0 or 1) is guarded so the slow path no longer enters
its run-past loop.

All four variants are now bit-exact with the C reference for even and odd
widths. Verified with checkasm under qemu-aarch64.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit a554d0aa8a)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer
2026-06-15 22:12:41 +02:00
parent 11b24e9b93
commit db8b450ebb
1 changed files with 79 additions and 0 deletions
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79
libswscale/aarch64/rgb2rgb_neon.S
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@@ -611,11 +611,78 @@ w17 - set to 1 if last line has to be handled separately (odd height)
add x2, x2, x7
.endm
// width is processed in whole pixel pairs; if the original width was odd this
// emits the trailing column for one line, matching the C reference. w15 holds
// the odd-width flag, the pointers are at the end of the even part of the line.
.macro write_last_odd_column src_fmt, dst_fmt, is_final_odd_line=0, y_off=0
.ifc \dst_fmt, yuv422
cbz w15, 0f
.ifc \src_fmt, uyvy
ldrb w12, [x3, #1] // Y = src[2w-1]
strb w12, [x0]
ldrb w12, [x3] // U = src[2w-2]
strb w12, [x1]
ldrb w12, [x3, #2] // V = src[2w]
strb w12, [x2]
.else
ldrb w12, [x3] // Y = src[2w-2]
strb w12, [x0]
ldrb w12, [x3, #1] // U = src[2w-1]
strb w12, [x1]
ldrb w12, [x3, #3] // V = src[2w+1]
strb w12, [x2]
.endif
0:
.endif
.ifc \dst_fmt, yuv420
cbz w15, 0f
.if \is_final_odd_line
ldrb w12, [x3, #\y_off] // luma only; chroma is skipped on the odd last line
strb w12, [x0]
.else
.ifc \src_fmt, uyvy
ldrb w12, [x3, #1] // Y, top line
strb w12, [x0]
ldrb w12, [x13, #1] // Y, bottom line
strb w12, [x10]
ldrb w12, [x3] // U = (top + bottom) >> 1
ldrb w14, [x13]
add w12, w12, w14
lsr w12, w12, #1
strb w12, [x1]
ldrb w12, [x3, #2] // V = (top + bottom) >> 1
ldrb w14, [x13, #2]
add w12, w12, w14
lsr w12, w12, #1
strb w12, [x2]
.else
ldrb w12, [x3] // Y, top line
strb w12, [x0]
ldrb w12, [x13] // Y, bottom line
strb w12, [x10]
ldrb w12, [x3, #1] // U = (top + bottom) >> 1
ldrb w14, [x13, #1]
add w12, w12, w14
lsr w12, w12, #1
strb w12, [x1]
ldrb w12, [x3, #3] // V = (top + bottom) >> 1
ldrb w14, [x13, #3]
add w12, w12, w14
lsr w12, w12, #1
strb w12, [x2]
.endif
.endif
0:
.endif
.endm
.macro interleaved_yuv_to_planar src_fmt, dst_fmt
function ff_\src_fmt\()to\dst_fmt\()_neon, export=1
sxtw x6, w6
sxtw x7, w7
ldrsw x8, [sp]
and w15, w4, #1 // odd width: trailing column via epilogue
bic w4, w4, #1 // process whole pixel pairs
ands w11, w4, #~31 // choose between fast and slow path
.ifc \dst_fmt, yuv420
@@ -641,6 +708,7 @@ function ff_\src_fmt\()to\dst_fmt\()_neon, export=1
b.ne 2b
fastpath_shift_back_pointers \src_fmt, \dst_fmt, 0
fastpath_iteration \src_fmt, \dst_fmt, 0, 0
write_last_odd_column \src_fmt, \dst_fmt
subs w5, w5, #1
move_pointers_to_next_line \src_fmt, \dst_fmt
b.ne 1b
@@ -653,16 +721,24 @@ function ff_\src_fmt\()to\dst_fmt\()_neon, export=1
b.ne 4b
fastpath_shift_back_pointers \src_fmt, \dst_fmt, 1
fastpath_iteration \src_fmt, \dst_fmt, 1, 1
.ifc \src_fmt, uyvy
write_last_odd_column \src_fmt, \dst_fmt, 1, 1
.else
write_last_odd_column \src_fmt, \dst_fmt, 1, 0
.endif
3:
.endif
ret
6: // slow path - width is at most 31
and w9, w4, #31
cbz w9, 9f // even part empty (orig width 0 or 1)
7:
subs w9, w9, #2
slowpath_iteration \src_fmt, \dst_fmt, 0
b.ne 7b
9:
write_last_odd_column \src_fmt, \dst_fmt
subs w5, w5, #1
move_pointers_to_next_line \src_fmt, \dst_fmt
b.ne 6b
@@ -673,10 +749,13 @@ function ff_\src_fmt\()to\dst_fmt\()_neon, export=1
.ifc \src_fmt, uyvy
add x3, x3, #1
.endif
cbz w9, 10f // even part empty (orig width 0 or 1)
5:
subs w9, w9, #2
slowpath_iteration \src_fmt, \dst_fmt, 1
b.ne 5b
10:
write_last_odd_column \src_fmt, \dst_fmt, 1, 0
8:
.endif
ret