/* * Project : tin - a Usenet reader * Module : newsrc.h * Author : I. Lea & R. Skrenta * Created : 1991-04-01 * Updated : 2024-09-27 * Notes : newsrc bit handling * * Copyright (c) 1997-2026 Iain Lea , Rich Skrenta * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright notice, * this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * 3. Neither the name of the copyright holder nor the names of its * contributors may be used to endorse or promote products derived from * this software without specific prior written permission. * * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. */ #ifndef NEWSRC_H #define NEWSRC_H 1 /* * The following macros are used to simplify and speed up the * manipulation of the bitmaps in memory which record which articles * are read or unread in each news group. * * Data representation: * * Each bitmap is handled as an array of bytes; the least-significant * bit of the 0th byte is the 0th bit; the most significant bit of * the 0th byte is the 7th bit. Thus, the most-significant bit of the * 128th byte is the 1023rd bit, and in general the mth bit of the nth * byte is considered to be bit (n*8)+m of the map as a whole. Conversely, * the position of bit q in the map is the bit (q & 7) of byte (q >> 3). * A bitmap of b bits will be allocated as ((b+7) >> 3) bytes. * * The routines could be changed to operate on a word-oriented bitmap by * changing the constants used from 8 to 16, 3 to 4, 7 to 15, etc. and * changing the allocate/deallocate routines. * * In the newsrc context, a 0 bit represents an article which is read * or expired; a 1 represents an unread article. The 0th bit corresponds * to the minimum article number for this group, and (max-min+7)/8 bytes * are allocated to the bitmap. * * Constants: * * NBITS = total number of bits per byte; * NMAXBIT = number of bits per byte or word; * NBITPOS = number of bit in NMAXBIT; * NBITSON = byte/word used to set all bits in byte/word to 1; * NBITNEG1 = binary negation of 1, used in constructing masks. * * Macro naming and use: * * The NOFFSET and NBITIDX macro construct the byte and bit indexes in * the map, given a bit number. * * The NSET0 macro sets a bit to binary 0 * The NSET1 macro sets a bit to binary 1 * The NSETBLK0 macro sets the same bit or bits to binary 0 * The NSETBLK1 macro sets the same bit or bits to binary 1 * The NTEST macro tests a single bit. * These are used frequently to access the group bitmap. * * NSETBLK0 and NSETBLK1 operate on whole numbers of bytes, and are * mainly useful for initializing complete bitmaps to one state or * another. Both use the memset function, which is assumed to be * optimized for the target architecture. NSETBLK is currently used to * initialize the group bitmap to 1s (unread). * * NSETRNG0 and NSETRNG1 operate on ranges of bits, from a low bit number * to a high bit number (inclusive), and are especially useful for * efficiently setting a contiguous range of bits to one state or another. * NSETRNG0 is currently used on the group bitmap to mark the ranges the * newsrc file says are read or expired. * * The algorithm is this. If the high number is less than the low, then * do nothing (error); if both fall within the same byte, construct a * single mask expressing the range and AND or OR it into the byte; else: * construct a mask for the byte containing the low bit, AND or OR it in; * use memset to fill in the intervening bytes efficiently; then construct * a mask for the byte containing the high bit, and AND or OR this mask * in. Masks are constructed by left-shift of 0xff (to set high-order bits * to 1), negating a left-shift of 0xfe (to set low-order bits to 1), and * the various negations and combinations of the same. This procedure is * complex, but 1 to 2 orders of magnitude faster than a shift inside a * loop for each bit inside a loop for each individual byte. * */ #define NBITS 8 #define NMAXBIT 7 #define NBITPOS 3 #define NBITSON 0xff #define NBITNEG1 0xfe #define NOFFSET(b) ((b) >> NBITPOS) #define NBITIDX(b) ((b) & NMAXBIT) #define NTEST(n,b) (n[NOFFSET(b)] & (1 << NBITIDX(b))) #if 0 /* unused */ #define NBITMASK(beg,end) (unsigned char) ~(((1 << (((NMAXBIT - beg) - (NMAXBIT - end)) + 1)) - 1) << (NMAXBIT - end)) #define NSETBLK1(n,i) (memset(n, NBITSON, (size_t) NOFFSET(i) + 1)) #define NSETBLK0(n,i) (memset(n, 0, (size_t) NOFFSET(i) + 1)) #endif /* 0 */ /* dbmalloc checks memset() parameters, so we'll use it to check the assignments */ #ifdef USE_DBMALLOC # define NSET1(n,b) memset(n + NOFFSET(b), n[NOFFSET(b)] | NTEST(n,b), 1) # define NSET0(n,b) memset(n + NOFFSET(b), n[NOFFSET(b)] & ~NTEST(n,b), 1) # define BIT_OR(n, b, mask) memset(n + NOFFSET(b), n[NOFFSET(b)] | (mask), 1) # define BIT_AND(n, b, mask) memset(n + NOFFSET(b), n[NOFFSET(b)] & (mask), 1) # include /* dbmalloc 1.4 */ #else # define NSET1(n,b) (n[NOFFSET(b)] |= (1 << NBITIDX(b))) # define NSET0(n,b) (n[NOFFSET(b)] &= 0xff & ~(1 << NBITIDX(b))) # define BIT_OR(n, b, mask) n[NOFFSET(b)] |= 0xff & mask # define BIT_AND(n, b, mask) n[NOFFSET(b)] &= 0xff & mask #endif /* USE_DBMALLOC */ #define BITS_TO_BYTES(n) ((size_t) ((n + NBITS - 1) / NBITS)) #endif /* !NEWSRC_H */