Remove QOI_DIFF_16 and QOI_DIFF_24; better tagging of remaining ops; better hash function
This commit is contained in:
parent
66d12eb078
commit
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282
qoi.h
282
qoi.h
@ -102,17 +102,23 @@ pixel value. Pixels are either encoded as
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A running array[64] of previously seen pixel values is maintained by the encoder
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and decoder. Each pixel that is seen by the encoder and decoder is put into this
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array at the position (r^g^b^a) % 64. In the encoder, if the pixel value at this
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index matches the current pixel, this index position is written to the stream.
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array at the position (r * 3 + g * 5 + b * 7) % 64. In the encoder, if the pixel
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value at this index matches the current pixel, this index position is written to
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the stream.
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Each chunk starts with a 2, 3 or 4 bit tag, followed by a number of data bits.
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Each chunk starts with a 8 or 2 bit tag, followed by a number of data bits.
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The bit length of chunks is divisible by 8 - i.e. all chunks are byte aligned.
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All values encoded in these data bits have the most significant bit (MSB) on the
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left.
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The 8-bit tags have precedence over the 2-bit tags. A decoder must check the
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8-bit tags first.
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The possible chunks are:
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- QOI_INDEX -------------
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- QOI_OP_INDEX ----------
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| Byte[0] |
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| 7 6 5 4 3 2 1 0 |
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|-------+-----------------|
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@ -122,23 +128,13 @@ The possible chunks are:
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6-bit index into the color index array: 0..63
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- QOI_RUN ---------------
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| Byte[0] |
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| 7 6 5 4 3 2 1 0 |
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|-------+-----------------|
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| 0 1 | run |
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2-bit tag b01
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6-bit run-length repeating the previous pixel: 1..64
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- QOI_DIFF_8 ------------
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- QOI_OP_DIFF -----------
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| Byte[0] |
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| 7 6 5 4 3 2 1 0 |
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|-------+-----+-----+-----|
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| 1 0 | dr | db | bg |
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| 0 1 | dr | dg | db |
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2-bit tag b10
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2-bit tag b01
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2-bit red channel difference from the previous pixel between -2..1
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2-bit green channel difference from the previous pixel between -2..1
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2-bit blue channel difference from the previous pixel between -2..1
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@ -147,31 +143,16 @@ The difference to the current channel values are using a wraparound operation,
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so "1 - 2" will result in 255, while "255 + 1" will result in 0.
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- QOI_DIFF_16 -------------------------------------
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- QOI_OP_LUMA -------------------------------------
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| Byte[0] | Byte[1] |
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| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
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|-------------+-----------|------------ +-----------|
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| 1 1 0 0 | red diff | green diff | blue diff |
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|-------+-----------------+-------------+-----------|
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| 1 0 | green diff | dr - dg | db - dg |
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4-bit tag b1100
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4-bit red channel difference from the previous pixel between -8..7
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4-bit green channel difference from the previous pixel between -8..7
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4-bit blue channel difference from the previous pixel between -8..7
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The difference to the current channel values are using a wraparound operation,
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so "5 - 8" will result in 253, while "250 + 7" will result in 1.
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- QOI_GDIFF_16 ------------------------------------
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| Byte[0] | Byte[1] |
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| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
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|-------------+--------+-------------------+--------|
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| 1 1 0 1 | dr-dg | green diff | db-dg |
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4-bit tag b1101
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3-bit red channel difference minus green channel difference -4..3
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2-bit tag b10
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6-bit green channel difference from the previous pixel -32..31
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3-bit blue channel difference minus green channel difference -4..3
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4-bit red channel difference minus green channel difference -8..7
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4-bit blue channel difference minus green channel difference -8..7
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The green channel is used to indicate the general direction of change and gets
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a few more bits. dr and db base their diffs off of the green channel diff. E.g.
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@ -181,42 +162,46 @@ The difference to the current channel values are using a wraparound operation,
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so "10 - 13" will result in 253, while "250 + 7" will result in 1.
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- QOI_DIFF_24 ---------------------------------------------------------------
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| Byte[0] | Byte[1] | Byte[2] |
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| 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 | 7 6 5 4 3 2 1 0 |
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|-------------+----------------+--------------+----------------+--------------|
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| 1 1 1 0 | red diff | green diff | blue diff | alpha diff |
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4-bit tag b1110
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5-bit red channel difference from the previous pixel between -16..15
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5-bit green channel difference from the previous pixel between -16..15
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5-bit blue channel difference from the previous pixel between -16..15
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5-bit alpha channel difference from the previous pixel between -16..15
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The difference to the current channel values are using a wraparound operation,
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so "10 - 13" will result in 253, while "250 + 7" will result in 1.
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- QOI_COLOR -------------
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- QOI_OP_RUN ------------
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| Byte[0] |
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| 7 6 5 4 3 2 1 0 |
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|-------------+--+--+--+--|
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| 1 1 1 1 |hr|hg|hb|ha|
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|-------+-----------------|
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| 1 1 | run |
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4-bit tag b1111
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1-bit red byte follows
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1-bit green byte follows
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1-bit blue byte follows
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1-bit alpha byte follows
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For each set bit hr, hg, hb and ha another byte follows in this order. If such a
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byte follows, it will replace the current color channel value with the value of
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this byte.
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2-bit tag b01
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6-bit run-length repeating the previous pixel: 1..62
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Note that the run-lengths 63 and 64 (b111110 and b111111) are illegal as they
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are occupied by the QOI_OP_RGB and QOI_OP_RGBA tags.
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The byte stream is padded at the end with 4 zero bytes. Size the longest chunk
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we can encounter is 5 bytes (QOI_COLOR with RGBA set), with this padding we just
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have to check for an overrun once per decode loop iteration.
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- QOI_OP_RGB ------------------------------------------
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| Byte[0] | Byte[1] | Byte[2] | Byte[3] |
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| 7 6 5 4 3 2 1 0 | 7 .. 0 | 7 .. 0 | 7 .. 0 |
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|-------------------------+---------+---------+---------|
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| 1 1 1 1 1 1 1 0 | red | green | blue |
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8-bit tag b11111110
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8-bit red channel value
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8-bit green channel value
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8-bit blue channel value
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- QOI_OP_RGBA ----------------------------------------------------
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| Byte[0] | Byte[1] | Byte[2] | Byte[3] | Byte[4] |
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| 7 6 5 4 3 2 1 0 | 7 .. 0 | 7 .. 0 | 7 .. 0 | 7 .. 0 |
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|-------------------------+---------+---------+---------+---------|
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| 1 1 1 1 1 1 1 1 | red | green | blue | alpha |
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8-bit tag b11111111
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8-bit red channel value
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8-bit green channel value
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8-bit blue channel value
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8-bit alpha channel value
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The byte stream is padded at the end with 4 zero bytes. Size the longest legal
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chunk is 5 bytes (QOI_OP_RGBA), with this padding it is possible to check for an
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overrun only once per decode loop iteration.
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*/
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@ -318,18 +303,16 @@ void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels);
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#define QOI_FREE(p) free(p)
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#endif
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#define QOI_INDEX 0x00 // 00xxxxxx
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#define QOI_RUN 0x40 // 01xxxxxx
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#define QOI_DIFF_8 0x80 // 10xxxxxx
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#define QOI_DIFF_16 0xc0 // 1100xxxx
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#define QOI_GDIFF_16 0xd0 // 1101xxxx
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#define QOI_DIFF_24 0xe0 // 1110xxxx
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#define QOI_COLOR 0xf0 // 1111xxxx
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#define QOI_OP_INDEX 0x00 // 00xxxxxx
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#define QOI_OP_DIFF 0x40 // 01xxxxxx
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#define QOI_OP_LUMA 0x80 // 10xxxxxx
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#define QOI_OP_RUN 0xc0 // 11xxxxxx
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#define QOI_OP_RGB 0xfe // 11111110
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#define QOI_OP_RGBA 0xff // 11111111
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#define QOI_MASK_2 0xc0 // 11000000
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#define QOI_MASK_4 0xf0 // 11110000
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#define QOI_COLOR_HASH(C) (C.rgba.r ^ C.rgba.g ^ C.rgba.b ^ C.rgba.a)
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#define QOI_COLOR_HASH(C) (C.rgba.r * 3 + C.rgba.g * 5 + C.rgba.b * 7)
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#define QOI_MAGIC \
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(((unsigned int)'q') << 24 | ((unsigned int)'o') << 16 | \
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((unsigned int)'i') << 8 | ((unsigned int)'f'))
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@ -400,9 +383,9 @@ void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
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px = *(qoi_rgba_t *)(pixels + px_pos);
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}
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else {
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px.rgba.r = pixels[px_pos];
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px.rgba.g = pixels[px_pos+1];
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px.rgba.b = pixels[px_pos+2];
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px.rgba.r = pixels[px_pos + 0];
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px.rgba.g = pixels[px_pos + 1];
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px.rgba.b = pixels[px_pos + 2];
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}
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if (px.v == px_prev.v) {
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@ -411,9 +394,9 @@ void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
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if (
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run > 0 &&
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(run == 64 || px.v != px_prev.v || px_pos == px_end)
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(run == 62 || px.v != px_prev.v || px_pos == px_end)
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) {
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bytes[p++] = QOI_RUN | (run - 1);
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bytes[p++] = QOI_OP_RUN | (run - 1);
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run = 0;
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}
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@ -421,61 +404,47 @@ void *qoi_encode(const void *data, const qoi_desc *desc, int *out_len) {
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int index_pos = QOI_COLOR_HASH(px) % 64;
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if (index[index_pos].v == px.v) {
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bytes[p++] = QOI_INDEX | index_pos;
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bytes[p++] = QOI_OP_INDEX | index_pos;
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}
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else {
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index[index_pos] = px;
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char vr = px.rgba.r - px_prev.rgba.r;
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char vg = px.rgba.g - px_prev.rgba.g;
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char vb = px.rgba.b - px_prev.rgba.b;
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char va = px.rgba.a - px_prev.rgba.a;
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if (px.rgba.a == px_prev.rgba.a) {
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char vr = px.rgba.r - px_prev.rgba.r;
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char vg = px.rgba.g - px_prev.rgba.g;
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char vb = px.rgba.b - px_prev.rgba.b;
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char vg_r = vr - vg;
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char vg_b = vb - vg;
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char vg_r = vr - vg;
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char vg_b = vb - vg;
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if (
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va == 0 &&
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vr > -3 && vr < 2 &&
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vg > -3 && vg < 2 &&
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vb > -3 && vb < 2
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) {
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bytes[p++] = QOI_DIFF_8 | ((vr + 2) << 4) | (vg + 2) << 2 | (vb + 2);
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}
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else if (
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va == 0 &&
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vr > -9 && vr < 8 &&
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vg > -9 && vg < 8 &&
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vb > -9 && vb < 8
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) {
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bytes[p++] = QOI_DIFF_16 | (vr + 8);
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bytes[p++] = (vg + 8) << 4 | (vb + 8);
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}
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else if (
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va == 0 &&
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vg_r > -5 && vg_r < 4 &&
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vg > -33 && vg < 32 &&
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vg_b > -5 && vg_b < 4
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) {
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bytes[p++] = QOI_GDIFF_16 | (vg_r + 4) << 1 | (vg + 32) >> 5;
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bytes[p++] = (vg + 32) << 3 | (vg_b + 4);
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}
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else if (
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vr > -17 && vr < 16 &&
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vg > -17 && vg < 16 &&
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vb > -17 && vb < 16 &&
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va > -17 && va < 16
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) {
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bytes[p++] = QOI_DIFF_24 | (vr + 16) >> 1;
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bytes[p++] = (vr + 16) << 7 | (vg + 16) << 2 | (vb + 16) >> 3;
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bytes[p++] = (vb + 16) << 5 | (va + 16);
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if (
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vr > -3 && vr < 2 &&
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vg > -3 && vg < 2 &&
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vb > -3 && vb < 2
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) {
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bytes[p++] = QOI_OP_DIFF | ((vr + 2) << 4) | (vg + 2) << 2 | (vb + 2);
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}
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else if (
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vg_r > -9 && vg_r < 8 &&
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vg > -33 && vg < 32 &&
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vg_b > -9 && vg_b < 8
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) {
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bytes[p++] = QOI_OP_LUMA | (vg + 32);
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bytes[p++] = (vg_r + 8) << 4 | (vg_b + 8);
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}
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else {
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bytes[p++] = QOI_OP_RGB;
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bytes[p++] = px.rgba.r;
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bytes[p++] = px.rgba.g;
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bytes[p++] = px.rgba.b;
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}
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}
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else {
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bytes[p++] = QOI_COLOR | (vr ? 8 : 0) | (vg ? 4 : 0) | (vb ? 2 : 0) | (va ? 1 : 0);
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if (vr) { bytes[p++] = px.rgba.r; }
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if (vg) { bytes[p++] = px.rgba.g; }
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if (vb) { bytes[p++] = px.rgba.b; }
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if (va) { bytes[p++] = px.rgba.a; }
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bytes[p++] = QOI_OP_RGBA;
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bytes[p++] = px.rgba.r;
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bytes[p++] = px.rgba.g;
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bytes[p++] = px.rgba.b;
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bytes[p++] = px.rgba.a;
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}
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}
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}
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@ -538,43 +507,34 @@ void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels) {
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else if (p < chunks_len) {
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int b1 = bytes[p++];
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if ((b1 & QOI_MASK_2) == QOI_INDEX) {
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px = index[b1 ^ QOI_INDEX];
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if (b1 == QOI_OP_RGB) {
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px.rgba.r = bytes[p++];
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px.rgba.g = bytes[p++];
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px.rgba.b = bytes[p++];
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}
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else if ((b1 & QOI_MASK_2) == QOI_RUN) {
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run = (b1 & 0x3f);
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else if (b1 == QOI_OP_RGBA) {
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px.rgba.r = bytes[p++];
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px.rgba.g = bytes[p++];
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px.rgba.b = bytes[p++];
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px.rgba.a = bytes[p++];
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}
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else if ((b1 & QOI_MASK_2) == QOI_DIFF_8) {
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else if ((b1 & QOI_MASK_2) == QOI_OP_INDEX) {
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px = index[b1 ^ QOI_OP_INDEX];
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}
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else if ((b1 & QOI_MASK_2) == QOI_OP_DIFF) {
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px.rgba.r += ((b1 >> 4) & 0x03) - 2;
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px.rgba.g += ((b1 >> 2) & 0x03) - 2;
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px.rgba.b += ( b1 & 0x03) - 2;
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}
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else if ((b1 & QOI_MASK_4) == QOI_DIFF_16) {
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else if ((b1 & QOI_MASK_2) == QOI_OP_LUMA) {
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int b2 = bytes[p++];
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px.rgba.r += (b1 & 0x0f) - 8;
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px.rgba.g += (b2 >> 4) - 8;
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px.rgba.b += (b2 & 0x0f) - 8;
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}
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else if ((b1 & QOI_MASK_4) == QOI_GDIFF_16) {
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int b2 = bytes[p++];
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int vg = ((b1 & 0x01) << 5 | (b2 & 0xf8) >> 3) - 32;
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px.rgba.r += vg - 4 + ((b1 & 0x0e) >> 1);
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int vg = (b1 & 0x3f) - 32;
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px.rgba.r += vg - 8 + ((b2 >> 4) & 0x0f);
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px.rgba.g += vg;
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px.rgba.b += vg - 4 + (b2 & 0x07);
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px.rgba.b += vg - 8 + (b2 & 0x0f);
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}
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else if ((b1 & QOI_MASK_4) == QOI_DIFF_24) {
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int b2 = bytes[p++];
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int b3 = bytes[p++];
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px.rgba.r += (((b1 & 0x0f) << 1) | (b2 >> 7)) - 16;
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px.rgba.g += ((b2 & 0x7c) >> 2) - 16;
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px.rgba.b += (((b2 & 0x03) << 3) | ((b3 & 0xe0) >> 5)) - 16;
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px.rgba.a += (b3 & 0x1f) - 16;
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}
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else if ((b1 & QOI_MASK_4) == QOI_COLOR) {
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if (b1 & 8) { px.rgba.r = bytes[p++]; }
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if (b1 & 4) { px.rgba.g = bytes[p++]; }
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if (b1 & 2) { px.rgba.b = bytes[p++]; }
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if (b1 & 1) { px.rgba.a = bytes[p++]; }
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else if ((b1 & QOI_MASK_2) == QOI_OP_RUN) {
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run = (b1 & 0x3f);
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}
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index[QOI_COLOR_HASH(px) % 64] = px;
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@ -584,9 +544,9 @@ void *qoi_decode(const void *data, int size, qoi_desc *desc, int channels) {
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*(qoi_rgba_t*)(pixels + px_pos) = px;
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}
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else {
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pixels[px_pos] = px.rgba.r;
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pixels[px_pos+1] = px.rgba.g;
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pixels[px_pos+2] = px.rgba.b;
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pixels[px_pos + 0] = px.rgba.r;
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pixels[px_pos + 1] = px.rgba.g;
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pixels[px_pos + 2] = px.rgba.b;
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}
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}
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