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swscale/ops_internal: fix ff_sws_pack_op_decode()

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This function was assuming that the bits are MSB-aligned, but they are
LSB-aligned in both practice (and in the actual backend).

Also update the documentation of SwsPackOp to make this clearer.

Fixes an incorrect omission of a clamp after decoding e.g. rgb4, since
the max value range was incorrectly determined as 0 as a result of unpacking
the MSB bits instead of the LSB bits:

 bgr4 -> gray:
   [ u8 XXXX -> +XXX] SWS_OP_READ         : 1 elem(s) packed >> 1
   [ u8 .XXX -> +++X] SWS_OP_UNPACK       : {1 2 1 0}
   [ u8 ...X -> +++X] SWS_OP_SWIZZLE      : 2103
   [ u8 ...X -> +++X] SWS_OP_CONVERT      : u8 -> f32
   [f32 ...X -> .++X] SWS_OP_LINEAR       : dot3 [...]
   [f32 .XXX -> .++X] SWS_OP_DITHER       : 16x16 matrix + {0 3 2 5}
+  [f32 .XXX -> .++X] SWS_OP_MIN          : x <= {255 _ _ _}
   [f32 .XXX -> +++X] SWS_OP_CONVERT      : f32 -> u8
   [ u8 .XXX -> +++X] SWS_OP_WRITE        : 1 elem(s) planar >> 0
     (X = unused, + = exact, 0 = zero)
This commit is contained in:
Niklas Haas
2025-12-22 15:31:01 +01:00
committed by Niklas Haas
parent 6656b11a7b
commit fafd72ef04
3 changed files with 8 additions and 2 deletions
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tests/ref/fate/sws-ops-list
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