third_party/ulib/musl/src/stdio/ungetc.c

#include "stdio_impl.h"

int ungetc(int c, FILE* f) {
    if (c == EOF)
        return c;

    FLOCK(f);

    if (!f->rpos)
        __toread(f);
    if (!f->rpos || f->rpos <= f->buf - UNGET) {
        FUNLOCK(f);
        return EOF;
    }

    *--f->rpos = c;
    f->flags &= ~F_EOF;

    FUNLOCK(f);
    return c;
}