1 /*
2 * mix.cc --
3 *
4 * FIXME: This file needs a description here.
5 *
6 * Copyright (c) 1996-2002 The Regents of the University of California.
7 * All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions are met:
11 *
12 * A. Redistributions of source code must retain the above copyright notice,
13 * this list of conditions and the following disclaimer.
14 * B. Redistributions in binary form must reproduce the above copyright notice,
15 * this list of conditions and the following disclaimer in the documentation
16 * and/or other materials provided with the distribution.
17 * C. Neither the names of the copyright holders nor the names of its
18 * contributors may be used to endorse or promote products derived from this
19 * software without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
22 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
23 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
24 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
25 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
26 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
27 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
28 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
29 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
30 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
31 * POSSIBILITY OF SUCH DAMAGE.
32 */
33
34 /*
35 * This routine mixes the DC & AC components of an 8x8 block of
36 * pixels. This routine is called for every block decoded so it
37 * needs to be efficient. It tries to do as many pixels in parallel
38 * as will fit in a word. The one complication is that it has to
39 * deal with overflow (sum > 255) and underflow (sum < 0). Underflow
40 * & overflow are only possible if both terms have the same sign and
41 * are indicated by the result having a different sign than the terms.
42 * Note that underflow is more worrisome than overflow since it results
43 * in bright white dots in a black field.
44 * The DC term and sum are biased by 128 so a negative number has the
45 * 2^7 bit = 0. The AC term is not biased so a negative number has
46 * the 2^7 bit = 1. So underflow is indicated by (DC & AC & sum) != 0;
47 */
48 #define JPEG_MIX_LOGIC \
49 sum = dc + ac; \
50 uflo = (dc ^ ac) & (dc ^ sum) & omask; \
51 if (uflo) { \
52 if ((ac = uflo & dc) != 0) { \
53 /* integer overflows */ \
54 ac |= ac >> 1; \
55 ac |= ac >> 2; \
56 ac |= ac >> 4; \
57 sum |= ac; \
58 } \
59 if ((uflo &=~ ac) != 0) { \
60 /* integer underflow(s) */ \
61 uflo |= uflo >> 1; \
62 uflo |= uflo >> 2; \
63 uflo |= uflo >> 4; \
64 sum &= ~uflo; \
65 } \
66 }
67
68 #ifdef INT_64
69 #define JPEG_MIX8(bp, out) \
70 ac = *(INT_64*)(bp); \
71 JPEG_MIX_LOGIC \
72 *(INT_64*)(out) = sum; \
73 (bp) += 8; \
74 (out) += stride;
75 #else
76 #define JPEG_MIX4(bp, out) \
77 ac = *(u_word*)(bp); \
78 JPEG_MIX_LOGIC \
79 *(u_word*)(out) = sum;
80
81 #define JPEG_MIX8(bp, out) \
82 JPEG_MIX4(bp, out) \
83 JPEG_MIX4(bp + 4, out + 4) \
84 bp += 8; \
85 out += stride;
86 #endif
87
88
89 void JpegDecoder::mix(u_int idc, const u_char* bp, u_char* out, int stride) const
90 {
91 register int t;
92
93 idc = UCLIMIT(idc) & 0xff;
94 idc |= idc << 8;
95 idc |= idc << 16;
96 #ifdef INT_64
97 INT_64 dc = idc, ac, sum;
98 dc |= dc << 32;
99 INT_64 uflo, omask = 0x8080808080808080;
100 #else
101 u_word dc = idc, ac, sum;
102 u_word uflo, omask = 0x80808080;
103 #endif
104
105 JPEG_MIX8(bp, out)
106 JPEG_MIX8(bp, out)
107 JPEG_MIX8(bp, out)
108 JPEG_MIX8(bp, out)
109 JPEG_MIX8(bp, out)
110 JPEG_MIX8(bp, out)
111 JPEG_MIX8(bp, out)
112 JPEG_MIX8(bp, out)
113 }
114
115
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