third_party/musl/src/internal/shgetc.c

#include "shgetc.h"

/* The shcnt field stores the number of bytes read so far, offset by
 * the value of buf-rpos at the last function call (__shlim or __shgetc),
 * so that between calls the inline shcnt macro can add rpos-buf to get
 * the actual count. */

void __shlim(FILE *f, off_t lim)
{
	f->shlim = lim;
	f->shcnt = f->buf - f->rpos;
	/* If lim is nonzero, rend must be a valid pointer. */
	if (lim && f->rend - f->rpos > lim)
		f->shend = f->rpos + lim;
	else
		f->shend = f->rend;
}

int __shgetc(FILE *f)
{
	int c;
	off_t cnt = shcnt(f);
	if (f->shlim && cnt >= f->shlim || (c=__uflow(f)) < 0) {
		f->shcnt = f->buf - f->rpos + cnt;
		f->shend = f->rpos;
		f->shlim = -1;
		return EOF;
	}
	cnt++;
	if (f->shlim && f->rend - f->rpos > f->shlim - cnt)
		f->shend = f->rpos + (f->shlim - cnt);
	else
		f->shend = f->rend;
	f->shcnt = f->buf - f->rpos + cnt;
	if (f->rpos <= f->buf) f->rpos[-1] = c;
	return c;
}