[Someone]

Maybe, but that text says “as if” and even “If an error occurs, the resulting value of the file position indicator for the stream is indeterminate. If a partial element is read, its value is indeterminate.” so it doesn’t in any way require implementations to implement it by actually reading one byte at a time.

That description also fits what I saw in the implementations I inspected, both of which simply try to read size × count bytes.

[Joker_vD]

By the way, behold the original (from UNIX Version 7) stdio package [0]:

    fread(ptr, size, count, iop)
    unsigned size, count;
    register char *ptr;
    register FILE *iop;
    {
        register c;
        unsigned ndone, s;
    
        ndone = 0;
        if (size)
        for (; ndone<count; ndone++) {
            s = size;
            do {
                if ((c = getc(iop)) >= 0)
                    *ptr++ = c;
                else
                    return(ndone);
            } while (--s);
        }
        return(ndone);
    }

Thankfully, the definition of getc() [1] is indeed

    #define getc(p)  (--(p)->_cnt>=0? *(p)->_ptr++&0377:_filbuf(p))

Interestingly enough, because there is no explicit multiplication, this loop properly works on systems with e.g. 16-bit unsigned int but 32-bit pointers (and overflows just the same on systems where ints and pointers are the same size).

[0] https://github.com/v7unix/v7unix/blob/master/v7/usr/src/libc...

[1] https://github.com/v7unix/v7unix/blob/master/v7/usr/include/...