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1.1 root 1: #ifndef lint
2: static char *rcsid_reversebits_c = "$Header: reversebits.c,v 10.1 86/11/19 10:44:01 jg Exp $";
3: #endif lint
4: /* reversebits.c - bit reversal code
5: *
6: * ReverseCharBits reverse bits in each byte
7: * ReverseShortBits reverse bits in each short
8: *
9: * Author:
10: * Scott Bates
11: * Brown University
12: * IRIS, Box 1946
13: * Providence, RI 02912
14: *
15: *
16: * Copyright (c) 1986 Brown University
17: *
18: * Permission to use, copy, modify and distribute this software and its
19: * documentation for any purpose and without fee is hereby granted, provided
20: * that the above copyright notice appear in all copies, and that both
21: * that copyright notice and this permission notice appear in supporting
22: * documentation, and that the name of Brown University not be used in
23: * advertising or publicity pertaining to distribution of the software
24: * without specific, written prior permission. Brown University makes no
25: * representations about the suitability of this software for any purpose.
26: * It is provided "as-is" without express or implied warranty.
27: */
28:
29: #include "private.h"
30:
31: u_char BitsReversed[256] = {
32: 0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50,
33: 0xD0, 0x30, 0xB0, 0x70, 0xF0, 0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8,
34: 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8, 0x04,
35: 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4,
36: 0x34, 0xB4, 0x74, 0xF4, 0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C,
37: 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC, 0x02, 0x82,
38: 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32,
39: 0xB2, 0x72, 0xF2, 0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
40: 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA, 0x06, 0x86, 0x46,
41: 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6,
42: 0x76, 0xF6, 0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E,
43: 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE, 0x01, 0x81, 0x41, 0xC1,
44: 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71,
45: 0xF1, 0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99,
46: 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9, 0x05, 0x85, 0x45, 0xC5, 0x25,
47: 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
48: 0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D,
49: 0xDD, 0x3D, 0xBD, 0x7D, 0xFD, 0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3,
50: 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3, 0x0B,
51: 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB,
52: 0x3B, 0xBB, 0x7B, 0xFB, 0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67,
53: 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7, 0x0F, 0x8F,
54: 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F,
55: 0xBF, 0x7F, 0xFF
56: };
57:
58: /*
59: * reverse bits in each byte
60: */
61:
62: ReverseCharBits(charbits, charcount)
63: register u_char *charbits;
64: register charcount;
65: {
66: register u_char *bits = (u_char *) &BitsReversed[0];
67:
68: #ifdef TRACE_X
69: fprintf (stderr, "In ReverseCharBits\n");
70: fflush (stderr);
71: #endif TRACE_X
72:
73: /*
74: * Do table look-up for each byte
75: */
76:
77: do {
78: *charbits = *(bits + *charbits);
79: charbits++;
80: } while(--charcount);
81: }
82:
83: /*
84: * reverse bits in each short
85: */
86:
87: ReverseShortBits(shortbits, shortcount)
88: register u_short *shortbits;
89: register shortcount;
90: {
91: register u_char *bits = (u_char *) &BitsReversed[0];
92: register u_char *charbits = (u_char *) shortbits;
93: register u_short tmpbits;
94:
95: #ifdef TRACE_X
96: fprintf (stderr, "In ReverseShortBits\n");
97: fflush (stderr);
98: #endif TRACE_X
99:
100: do {
101: tmpbits = (u_short) *(bits + *charbits++);
102: tmpbits |= (u_short) (*(bits + *charbits++) << 8);
103: *shortbits++ = tmpbits;
104: } while(--shortcount);
105: }
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