simplify base64_encode()

src/base64.c

@@ -61,6 +61,7 @@ base64_encode(const enum encoding enc, char *restrict const buf,
 	const struct b64_alphabet *alpha = &b64_alphabet[enc];
 	char *p = buf;
 	const uint8_t *in = (uint8_t *)inbuf;
+	const uint8_t * const end = in + inlength;
 
 	AN(buf);
 	AN(alpha);
@@ -70,34 +71,30 @@ base64_encode(const enum encoding enc, char *restrict const buf,
 	    || maxlen < base64nopad_encode_l(inlength))
 		return -1;
 
-	while (in < (uint8_t *)inbuf + inlength) {
-		uint8_t idx;
-		size_t rest = ((uint8_t *)inbuf + inlength) - in;
-
+	while (end - in >= 3) {
 		*p++ = alpha->b64[(in[0] >> 2) & 0x3f];
-
-		idx = (in[0] << 4);
-		if (rest > 1)
-			idx += (in[1] >> 4);
-		*p++ = alpha->b64[idx & 0x3f];
-
-		if (rest > 1) {
-			idx = (in[1] << 2);
-			if (rest > 2)
-				idx += in[2] >> 6;
-			*p++ = alpha->b64[idx & 0x3f];
-		}
-		else if (alpha->padding)
-			*p++ = alpha->padding;
-
-		if (rest > 2)
-			*p++ = alpha->b64[in[2] & 0x3f];
-		else if (alpha->padding)
-			*p++ = alpha->padding;
-
+		*p++ = alpha->b64[((in[0] << 4) | (in[1] >> 4)) & 0x3f];
+		*p++ = alpha->b64[((in[1] << 2) | (in[2] >> 6)) & 0x3f];
+		*p++ = alpha->b64[in[2] & 0x3f];
 		in += 3;
 	}
-
+	if (end - in > 0) {
+		*p++ = alpha->b64[(in[0] >> 2) & 0x3f];
+		if (end - in == 1) {
+			*p++ = alpha->b64[(in[0] << 4) & 0x3f];
+			if (alpha->padding) {
+				*p++ = alpha->padding;
+				*p++ = alpha->padding;
+			}
+		}
+		else {
+			*p++ = alpha->b64[((in[0] << 4) | (in[1] >> 4)) & 0x3f];
+			*p++ = alpha->b64[(in[1] << 2) & 0x3f];
+			if (alpha->padding) {
+				*p++ = alpha->padding;
+			}
+		}
+	}
 	assert(p >= buf && p - buf <= maxlen);
 	return p - buf;
 }