better atomic fwrite_all internal

src/bits.c

@@ -15,13 +15,12 @@ static inline int sfread(void* out, size_t *restrict size, FILE* f)
 	return !!(*size = (size_t)fread(out, 1, *size, f));
 }
 
-static int fwrite_all(const void* buf, size_t esz, size_t num, FILE* out)
+static int fwrite_all(const void* _buf, size_t sz, size_t num, FILE* out)
 {
 	register size_t w, done=0;
-	register size_t fsz = esz * num;
-	const char* tbuf = (const char*)buf;
-	while( (w = fwrite(tbuf+done, 1, fsz-done, out)) > 0 && done < fsz) done+=w;
-	if (done!=fsz) return 0;
+	register const unsigned char* buf = _buf;
+	while( (w = fwrite(buf+done, sz, num-done, out)) > 0 && done < num) done+=w;
+	if (done!=num) return 0;
 	else return 1;
 }