encoding.base64: speed up encoding and decoding (#11055)

* add new function headers

* new encoding function

* rename to decode_micro and add helper functions

* implement new decoding function

* add test for buffer to buffer decoding

* - add notice to GO code
- v fmt base64.v

* implement new decoding function

* fix base64_memory_test.v by commenting a few lines

* vfmt base64.v

* add some more asserts to base64_memory_test.v

* remove unused decoding function

* add bounds check, when detecting the padding

* use union for storing the decoded data

Co-authored-by: Delyan Angelov <delian66@gmail.com>

vlib/encoding/base64/base64_memory_test.v

@@ -11,16 +11,37 @@ fn test_long_encoding() {
 	assert s_encoded.len > s_original.len
 	assert s_original == s_decoded
 
-	mut s := 0
-
 	ebuffer := unsafe { malloc(s_encoded.len) }
+	dbuffer := unsafe { malloc(s_decoded.len) }
+	//
+	encoded_size := base64.encode_in_buffer(s_original, ebuffer)
+	mut encoded_in_buf := []byte{len: encoded_size}
+	unsafe { C.memcpy(encoded_in_buf.data, ebuffer, encoded_size) }
+	assert input_size * 4 / 3 == encoded_size
+	assert encoded_in_buf[0] == `Y`
+	assert encoded_in_buf[1] == `W`
+	assert encoded_in_buf[2] == `F`
+	assert encoded_in_buf[3] == `h`
+
+	assert encoded_in_buf[encoded_size - 4] == `Y`
+	assert encoded_in_buf[encoded_size - 3] == `W`
+	assert encoded_in_buf[encoded_size - 2] == `F`
+	assert encoded_in_buf[encoded_size - 1] == `h`
+	assert encoded_in_buf == s_encoded.bytes()
+
+	decoded_size := base64.decode_in_buffer(s_encoded, dbuffer)
+	assert decoded_size == input_size
+	mut decoded_in_buf := []byte{len: decoded_size}
+	unsafe { C.memcpy(decoded_in_buf.data, dbuffer, decoded_size) }
+	assert decoded_in_buf == s_original
+
+	mut s := 0
 	for _ in 0 .. repeats {
 		resultsize := base64.encode_in_buffer(s_original, ebuffer)
 		s += resultsize
 		assert resultsize == s_encoded.len
 	}
 
-	dbuffer := unsafe { malloc(s_decoded.len) }
 	for _ in 0 .. repeats {
 		resultsize := base64.decode_in_buffer(s_encoded, dbuffer)
 		s += resultsize