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2 * Project : tin - a Usenet reader
3 * Module : newsrc.h
4 * Author : I. Lea & R. Skrenta
5 * Created : 1991-04-01
6 * Updated : 2003-11-18
7 * Notes : newsrc bit handling
9 * Copyright (c) 1997-2017 Iain Lea <email@example.com>, Rich Skrenta <firstname.lastname@example.org>
10 * All rights reserved.
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. The name of the author may not be used to endorse or promote
21 * products derived from this software without specific prior written
22 * permission.
24 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
25 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
26 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
28 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
30 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
31 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
32 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
33 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
34 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
37 #ifndef NEWSRC_H
38 #define NEWSRC_H 1
41 * The following macros are used to simplify and speed up the
42 * manipulation of the bitmaps in memory which record which articles
43 * are read or unread in each news group.
45 * Data representation:
47 * Each bitmap is handled as an array of bytes; the least-significant
48 * bit of the 0th byte is the 0th bit; the most significant bit of
49 * the 0th byte is the 7th bit. Thus, the most-significant bit of the
50 * 128th byte is the 1023rd bit, and in general the mth bit of the nth
51 * byte is considered to be bit (n*8)+m of the map as a whole. Conversely,
52 * the position of bit q in the map is the bit (q & 7) of byte (q >> 3).
53 * A bitmap of b bits will be allocated as ((b+7) >> 3) bytes.
55 * The routines could be changed to operate on a word-oriented bitmap by
56 * changing the constants used from 8 to 16, 3 to 4, 7 to 15, etc. and
57 * changing the allocate/deallocate routines.
59 * In the newsrc context, a 0 bit represents an article which is read
60 * or expired; a 1 represents an unread article. The 0th bit corresponds
61 * to the minimum article number for this group, and (max-min+7)/8 bytes
62 * are allocated to the bitmap.
64 * Constants:
66 * NBITS = total number of bits per byte;
67 * NMAXBIT = number of bits per byte or word;
68 * NBITPOS = number of bit in NMAXBIT;
69 * NBITSON = byte/word used to set all bits in byte/word to 1;
70 * NBITNEG1 = binary negation of 1, used in constructing masks.
72 * Macro naming and use:
74 * The NOFFSET and NBITIDX macro construct the byte and bit indexes in
75 * the map, given a bit number.
77 * The NSET0 macro sets a bit to binary 0
78 * The NSET1 macro sets a bit to binary 1
79 * The NSETBLK0 macro sets the same bit or bits to binary 0
80 * The NSETBLK1 macro sets the same bit or bits to binary 1
81 * The NTEST macro tests a single bit.
82 * These are used frequently to access the group bitmap.
84 * NSETBLK0 and NSETBLK1 operate on whole numbers of bytes, and are
85 * mainly useful for initializing complete bitmaps to one state or
86 * another. Both use the memset function, which is assumed to be
87 * optimized for the target architecture. NSETBLK is currently used to
88 * initialize the group bitmap to 1s (unread).
90 * NSETRNG0 and NSETRNG1 operate on ranges of bits, from a low bit number
91 * to a high bit number (inclusive), and are especially useful for
92 * efficiently setting a contiguous range of bits to one state or another.
93 * NSETRNG0 is currently used on the group bitmap to mark the ranges the
94 * newsrc file says are read or expired.
96 * The algorithm is this. If the high number is less than the low, then
97 * do nothing (error); if both fall within the same byte, construct a
98 * single mask expressing the range and AND or OR it into the byte; else:
99 * construct a mask for the byte containing the low bit, AND or OR it in;
100 * use memset to fill in the intervening bytes efficiently; then construct
101 * a mask for the byte containing the high bit, and AND or OR this mask
102 * in. Masks are constructed by left-shift of 0xff (to set high-order bits
103 * to 1), negating a left-shift of 0xfe (to set low-order bits to 1), and
104 * the various negations and combinations of the same. This procedure is
105 * complex, but 1 to 2 orders of magnitude faster than a shift inside a
106 * loop for each bit inside a loop for each individual byte.
109 #define NBITS 8
110 #define NMAXBIT 7
111 #define NBITPOS 3
112 #define NBITSON 0xff
113 #define NBITNEG1 0xfe
114 #define NOFFSET(b) ((b) >> NBITPOS)
115 #define NBITIDX(b) ((b) & NMAXBIT)
117 #define NBITMASK(beg,end) (unsigned char) ~(((1 << (((NMAXBIT - beg) - (NMAXBIT - end)) + 1)) - 1) << (NMAXBIT - end))
119 #define NTEST(n,b) (n[NOFFSET(b)] & (1 << NBITIDX(b)))
121 #define NSETBLK1(n,i) (memset(n, NBITSON, (size_t) NOFFSET(i) + 1))
122 #define NSETBLK0(n,i) (memset(n, 0, (size_t) NOFFSET(i) + 1))
124 /* dbmalloc checks memset() parameters, so we'll use it to check the assignments */
125 #ifdef USE_DBMALLOC
126 # define NSET1(n,b) memset(n + NOFFSET(b), n[NOFFSET(b)] | NTEST(n,b), 1)
127 # define NSET0(n,b) memset(n + NOFFSET(b), n[NOFFSET(b)] & ~NTEST(n,b), 1)
128 # define BIT_OR(n, b, mask) memset(n + NOFFSET(b), n[NOFFSET(b)] | (mask), 1)
129 # define BIT_AND(n, b, mask) memset(n + NOFFSET(b), n[NOFFSET(b)] & (mask), 1)
130 # include <dbmalloc.h> /* dbmalloc 1.4 */
132 # define NSET1(n,b) (n[NOFFSET(b)] |= (1 << NBITIDX(b)))
133 # define NSET0(n,b) (n[NOFFSET(b)] &= ~(1 << NBITIDX(b)))
134 # define BIT_OR(n, b, mask) n[NOFFSET(b)] |= mask
135 # define BIT_AND(n, b, mask) n[NOFFSET(b)] &= mask
136 #endif /* USE_DBMALLOC */
138 #define BITS_TO_BYTES(n) ((size_t) ((n + NBITS - 1) / NBITS))
140 #endif /* !NEWSRC_H */