/* $NetBSD: ch.c,v 1.6 2003/10/13 14:34:25 agc Exp $ */ /* * Copyright (c) 1988 Mark Nudelman * Copyright (c) 1988, 1993 * The Regents of the University of California. 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 University 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 REGENTS AND CONTRIBUTORS ``AS IS'' 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 REGENTS 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. */ #include <sys/cdefs.h> #ifndef lint #if 0 static char sccsid[] = "@(#)ch.c 8.1 (Berkeley) 6/6/93"; #else __RCSID("$NetBSD: ch.c,v 1.6 2003/10/13 14:34:25 agc Exp $"); #endif #endif /* not lint */ /* * Low level character input from the input file. * We use these special purpose routines which optimize moving * both forward and backward from the current read pointer. */ #include <sys/types.h> #include <sys/file.h> #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <err.h> #include "less.h" #include "extern.h" int file = -1; /* File descriptor of the input file */ /* * Pool of buffers holding the most recently used blocks of the input file. */ struct buf { struct buf *next, *prev; long block; int datasize; char data[BUFSIZ]; }; int nbufs; /* * The buffer pool is kept as a doubly-linked circular list, in order from * most- to least-recently used. The circular list is anchored by buf_anchor. */ #define END_OF_CHAIN ((struct buf *)&buf_anchor) #define buf_head buf_anchor.next #define buf_tail buf_anchor.prev static struct { struct buf *next, *prev; } buf_anchor = { END_OF_CHAIN, END_OF_CHAIN }; /* * Current position in file. * Stored as a block number and an offset into the block. */ static long ch_block; static int ch_offset; /* Length of file, needed if input is a pipe. */ static off_t ch_fsize; /* Number of bytes read, if input is standard input (a pipe). */ static off_t last_piped_pos; /* * Get the character pointed to by the read pointer. ch_get() is a macro * which is more efficient to call than fch_get (the function), in the usual * case that the block desired is at the head of the chain. */ #define ch_get() \ ((buf_head->block == ch_block && \ ch_offset < buf_head->datasize) ? \ buf_head->data[ch_offset] : fch_get()) static int fch_get __P((void)); static int buffered __P((long)); static int fch_get() { struct buf *bp; int n, ch; char *p, *t; off_t pos; /* look for a buffer holding the desired block. */ for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next) if (bp->block == ch_block) { if (ch_offset >= bp->datasize) /* * Need more data in this buffer. */ goto read_more; /* * On a pipe, we don't sort the buffers LRU * because this can cause gaps in the buffers. * For example, suppose we've got 12 1K buffers, * and a 15K input stream. If we read the first 12K * sequentially, then jump to line 1, then jump to * the end, the buffers have blocks 0,4,5,6,..,14. * If we then jump to line 1 again and try to * read sequentially, we're out of luck when we * get to block 1 (we'd get the "pipe error" below). * To avoid this, we only sort buffers on a pipe * when we actually READ the data, not when we * find it already buffered. */ if (ispipe) return(bp->data[ch_offset]); goto found; } /* * Block is not in a buffer. Take the least recently used buffer * and read the desired block into it. If the LRU buffer has data * in it, and input is a pipe, then try to allocate a new buffer first. */ if (ispipe && buf_tail->block != (long)(-1)) (void)ch_addbuf(1); bp = buf_tail; bp->block = ch_block; bp->datasize = 0; read_more: pos = (ch_block * BUFSIZ) + bp->datasize; if (ispipe) { /* * The data requested should be immediately after * the last data read from the pipe. */ if (pos != last_piped_pos) { error("pipe error"); quit(); } } else (void)lseek(file, pos, L_SET); /* * Read the block. * If we read less than a full block, we just return the * partial block and pick up the rest next time. */ n = iread(file, &bp->data[bp->datasize], BUFSIZ - bp->datasize); if (n == READ_INTR) return (EOI); if (n < 0) { error("read error"); quit(); } if (ispipe) last_piped_pos += n; p = &bp->data[bp->datasize]; bp->datasize += n; /* * Set an EOI marker in the buffered data itself. Then ensure the * data is "clean": there are no extra EOI chars in the data and * that the "meta" bit (the 0200 bit) is reset in each char; * also translate \r\n sequences to \n if -u flag not set. */ if (n == 0) { ch_fsize = pos; bp->data[bp->datasize++] = EOI; } if (bs_mode) { for (p = &bp->data[bp->datasize]; --n >= 0;) { *--p &= 0177; if (*p == EOI) *p = 0200; } } else { for (t = p; --n >= 0; ++p) { ch = *p & 0177; if (ch == '\r' && n && (p[1] & 0177) == '\n') { ++p; *t++ = '\n'; } else *t++ = (ch == EOI) ? 0200 : ch; } if (p != t) { bp->datasize -= p - t; if (ispipe) last_piped_pos -= p - t; } } found: if (buf_head != bp) { /* * Move the buffer to the head of the buffer chain. * This orders the buffer chain, most- to least-recently used. */ bp->next->prev = bp->prev; bp->prev->next = bp->next; bp->next = buf_head; bp->prev = END_OF_CHAIN; buf_head->prev = bp; buf_head = bp; } if (ch_offset >= bp->datasize) /* * After all that, we still don't have enough data. * Go back and try again. */ goto read_more; return(bp->data[ch_offset]); } /* * Determine if a specific block is currently in one of the buffers. */ static int buffered(block) long block; { struct buf *bp; for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next) if (bp->block == block) return(1); return(0); } /* * Seek to a specified position in the file. * Return 0 if successful, non-zero if can't seek there. */ int ch_seek(pos) off_t pos; { long new_block; new_block = pos / BUFSIZ; if (!ispipe || pos == last_piped_pos || buffered(new_block)) { /* * Set read pointer. */ ch_block = new_block; ch_offset = pos % BUFSIZ; return(0); } return(1); } /* * Seek to the end of the file. */ int ch_end_seek() { if (!ispipe) return(ch_seek(ch_length())); /* * Do it the slow way: read till end of data. */ while (ch_forw_get() != EOI) if (sigs) return(1); return(0); } /* * Seek to the beginning of the file, or as close to it as we can get. * We may not be able to seek there if input is a pipe and the * beginning of the pipe is no longer buffered. */ int ch_beg_seek() { struct buf *bp, *firstbp; /* * Try a plain ch_seek first. */ if (ch_seek((off_t)0) == 0) return(0); /* * Can't get to position 0. * Look thru the buffers for the one closest to position 0. */ firstbp = bp = buf_head; if (bp == END_OF_CHAIN) return(1); while ((bp = bp->next) != END_OF_CHAIN) if (bp->block < firstbp->block) firstbp = bp; ch_block = firstbp->block; ch_offset = 0; return(0); } /* * Return the length of the file, if known. */ off_t ch_length() { if (ispipe) return(ch_fsize); return((off_t)(lseek(file, (off_t)0, L_XTND))); } /* * Return the current position in the file. */ off_t ch_tell() { return(ch_block * BUFSIZ + ch_offset); } /* * Get the current char and post-increment the read pointer. */ int ch_forw_get() { int c; c = ch_get(); if (c != EOI && ++ch_offset >= BUFSIZ) { ch_offset = 0; ++ch_block; } return(c); } /* * Pre-decrement the read pointer and get the new current char. */ int ch_back_get() { if (--ch_offset < 0) { if (ch_block <= 0 || (ispipe && !buffered(ch_block-1))) { ch_offset = 0; return(EOI); } ch_offset = BUFSIZ - 1; ch_block--; } return(ch_get()); } /* * Allocate buffers. * Caller wants us to have a total of at least want_nbufs buffers. * keep==1 means keep the data in the current buffers; * otherwise discard the old data. */ void ch_init(want_nbufs, keep) int want_nbufs; int keep; { struct buf *bp; char message[80]; cbufs = nbufs; if (nbufs < want_nbufs && ch_addbuf(want_nbufs - nbufs)) { /* * Cannot allocate enough buffers. * If we don't have ANY, then quit. * Otherwise, just report the error and return. */ (void)snprintf(message, sizeof(message), "cannot allocate %d buffers", want_nbufs - nbufs); error(message); if (nbufs == 0) quit(); return; } if (keep) return; /* * We don't want to keep the old data, * so initialize all the buffers now. */ for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next) bp->block = (long)(-1); last_piped_pos = (off_t)0; ch_fsize = NULL_POSITION; (void)ch_seek((off_t)0); } /* * Allocate some new buffers. * The buffers are added to the tail of the buffer chain. */ int ch_addbuf(nnew) int nnew; { struct buf *bp; struct buf *newbufs; /* * We don't have enough buffers. * Allocate some new ones. */ newbufs = (struct buf *)calloc((u_int)nnew, sizeof(struct buf)); if (newbufs == NULL) return(1); /* * Initialize the new buffers and link them together. * Link them all onto the tail of the buffer list. */ nbufs += nnew; cbufs = nbufs; for (bp = &newbufs[0]; bp < &newbufs[nnew]; bp++) { bp->next = bp + 1; bp->prev = bp - 1; bp->block = (long)(-1); } newbufs[nnew-1].next = END_OF_CHAIN; newbufs[0].prev = buf_tail; buf_tail->next = &newbufs[0]; buf_tail = &newbufs[nnew-1]; return(0); }
