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/*
* 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 <iain@bricbrac.de>, Rich Skrenta <skrenta@pbm.com>
* 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.h> /* 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 */
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