Provide buffered fread(3)
In order to reduce calls to seek(2) (which are very expensive), this commit keeps a sector-sized cache for each available FILE instance, except from the standard streams, of course. As expected, this allows calls to fread(3) to react much faster when small, contiguous chunks are read.
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@ -70,6 +70,12 @@ typedef struct
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unsigned int eof;
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/** Error marker */
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unsigned int error;
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/** Sector buffer. */
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unsigned char *const buf;
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/** Last used sector for reading. */
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size_t last_sect;
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/** Sector buffer can be used for reading. */
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unsigned int cache_available;
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}FILE;
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extern FILE *const stdin, *const stdout, *const stderr;
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@ -111,7 +117,7 @@ int vprintf(const char *fmt, va_list ap);
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FILE *fdopen(int fildes, const char *mode);
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FILE *fopen(const char *path, const char *mode);
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int fclose(FILE *stream);
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int fread(void *ptr, int size, int nmemb, FILE *f);
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size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
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size_t fwrite(void *ptr, size_t size, size_t nmemb, FILE *stream);
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int fgetc(FILE *f);
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@ -19,13 +19,14 @@
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#include <errno.h>
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#include <unistd.h>
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char onesec_buf[2048];
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int errno;
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int __stdio_direction = STDIO_DIRECTION_BIOS;
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static unsigned int __sio_cr_mapped = 0;
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#define NUM_OF_FILE_STRUCTS 6
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enum {SECTOR_SZ = 2048};
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static FILE file_structs[NUM_OF_FILE_STRUCTS] =
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{
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[0] = // stdin
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@ -61,6 +62,11 @@ static FILE file_structs[NUM_OF_FILE_STRUCTS] =
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.eof = 0,
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.error = 0
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},
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[3 ... NUM_OF_FILE_STRUCTS - 1] =
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{
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.buf = (unsigned char[SECTOR_SZ]){}
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}
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};
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FILE *const stdin = &file_structs[0];
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@ -134,10 +140,20 @@ FILE *fdopen(int fildes, const char *mode)
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// Find a free file structure
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for(x = 0; x < NUM_OF_FILE_STRUCTS; x++)
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{
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if(file_structs[x].used == 0)
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FILE *const f = &file_structs[x];
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if(f->used == 0)
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{
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bzero(&file_structs[x], sizeof(FILE));
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file_structs[x].used = 1;
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f->size = 0;
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f->eof = 0;
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f->error = 0;
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f->used = 1;
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f->last_sect = 0;
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f->cache_available = 0;
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if (f->buf)
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memset(f->buf, 0, SECTOR_SZ);
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break;
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}
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}
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@ -230,6 +246,110 @@ int fclose(FILE *stream)
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return 0;
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}
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static size_t cdromread(void *restrict ptr, size_t sz,
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FILE *restrict const f)
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{
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const size_t start_sect = f->pos >> __builtin_ctz(SECTOR_SZ);
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const size_t end_pos = f->pos + sz;
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const size_t end_sector = end_pos >> __builtin_ctz(SECTOR_SZ);
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size_t readb = 0;
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int read_complete_sector = 0;
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if (feof(f) || ferror(f))
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return 0;
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else if (f->cache_available)
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{
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const size_t first_sector_sz = f->pos % SECTOR_SZ;
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if (f->last_sect == start_sect && f->last_sect == end_sector)
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{
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/* Use buffered I/O. */
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size_t max;
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if (end_pos >= f->size)
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{
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max = f->size - f->pos;
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f->eof = 1;
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}
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else
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{
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max = sz;
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}
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memcpy(ptr, &f->buf[first_sector_sz], max);
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f->pos += max;
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readb = max;
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}
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else if (f->last_sect == start_sect)
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{
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/* Partial buffered I/O possible. */
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const size_t firstsz = SECTOR_SZ - first_sector_sz;
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memcpy(ptr, &f->buf[first_sector_sz], firstsz);
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f->pos += firstsz;
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lseek(f->fildes, f->pos, SEEK_SET);
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f->cache_available = 0;
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readb += firstsz;
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read_complete_sector = 1;
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}
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}
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const size_t rem = sz - readb;
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if (rem)
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{
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const size_t whole_sectors = rem / SECTOR_SZ;
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if (whole_sectors)
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{
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if (!read_complete_sector)
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lseek(f->fildes, f->pos & ~(SECTOR_SZ - 1), SEEK_SET);
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const size_t s = whole_sectors * SECTOR_SZ;
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const int n = read(f->fildes, &((unsigned char *)ptr)[readb], s);
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if (n >= 0)
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{
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readb += s;
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f->pos += s;
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ptr = (unsigned char *)ptr + s;
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if (f->pos >= f->size)
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f->eof = 1;
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f->cache_available = 1;
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}
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}
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if (f->pos < f->size)
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{
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int n;
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if (!read_complete_sector)
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lseek(f->fildes, f->pos & ~(SECTOR_SZ - 1), SEEK_SET);
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n = read(f->fildes, f->buf, SECTOR_SZ);
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if (n >= 0)
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{
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readb = n > rem ? rem : n;
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memmove(ptr, f->buf, readb);
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ptr = (unsigned char *)ptr + readb;
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f->pos += readb;
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if (f->pos >= f->size)
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f->eof = 1;
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f->cache_available = 1;
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}
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}
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}
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f->last_sect = end_sector;
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return f->pos;
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}
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/*
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* fread doesn't require reads to be carried in block unit
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* Notice that however seeks on the CD drive will be very slow - so avoid using non block units
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@ -237,83 +357,29 @@ int fclose(FILE *stream)
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* This is done to make programming and porting easier
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*/
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int fread(void *ptr, int size, int nmemb, FILE *f)
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size_t fread(void *restrict const ptr, const size_t size, const size_t nmemb,
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FILE *restrict const f)
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{
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int rsize = size * nmemb;
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int csize = rsize;
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int max;
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int nsect = (f->pos + rsize) >> 11;
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nsect -= f->pos >> 11;
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nsect++;
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//printf("f->dev = %d, f->pos = %d, rsize = %d\n", f->dev, f->pos, rsize);
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if(f->dev == FDEV_CDROM)
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if (size && nmemb)
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{
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// First sector
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lseek(f->fildes, f->pos & (~0x7ff), SEEK_SET);
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read(f->fildes, onesec_buf, 2048);
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size_t rsize = size * nmemb;
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max = 2048 - (f->pos & 2047);
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//printf("ptr(FIRST) = %d, %x\n", ptr, ptr);
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printf("rsize = %d\n", rsize);
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memcpy(ptr, onesec_buf + (f->pos & 2047), (rsize > max) ? max : rsize);
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// Middle sector
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ptr += max;
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//printf("ptr(MIDDLEsex) = %d, %x\n", ptr, ptr);
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nsect--;
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csize -= max;
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if(nsect > 1)
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switch (f->dev)
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{
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//lseek(f->fildes, (f->pos & (~0x7ff)) + 2048, SEEK_SET);
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case FDEV_CDROM:
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rsize = cdromread(ptr, rsize, f);
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break;
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//#warning "Check correctness of this calculation."
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/*if(rsize & 2047)
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sect_num = (rsize|2047)+1;
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else
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sect_num = rsize;
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sect_num -= 4096;*/
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//printf("read_middle=%d, sect_num = %d\n", read(f->fildes, ptr, sect_num), sect_num);
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read(f->fildes, ptr, (nsect - 1) * 2048);
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ptr += (nsect - 1) * 2048;
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csize -= (nsect - 1) * 2048;
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nsect = 1;
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case FDEV_CONSOLE:
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/* Fall through. */
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default:
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return 0;
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}
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//printf("ptr(LAST) = %d, %x\n", ptr, ptr);
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if(nsect == 1)
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{
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// Last sector
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read(f->fildes, onesec_buf, 2048);
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memcpy(ptr, onesec_buf, csize);
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}
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}
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else if(f->dev == FDEV_CONSOLE)
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return 0;
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if(f->dev != FDEV_CONSOLE)
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{
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f->pos+= rsize;
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f->eof = (f->pos > f->size);
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if(f->eof)
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f->pos = f->size;
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return rsize / size;
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}
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return rsize;
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return 0;
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}
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int fgetc(FILE *f)
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