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/*
`Base64` encoding and decoding.
A secondary param can be used to supply a custom alphabet to `encode` and a matching decoding table to `decode`.
If none is supplied it just uses the standard Base64 alphabet.
In case your specific version does not use padding, you may
truncate it from the encoded output.
*/
package encoding_base64
import "core:io"
import "core:mem"
import "core:strings"
ENC_TABLE := [64]byte {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
'w', 'x', 'y', 'z', '0', '1', '2', '3',
'4', '5', '6', '7', '8', '9', '+', '/',
}
PADDING :: '='
DEC_TABLE := [128]int {
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, 62, -1, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59,
60, 61, -1, -1, -1, -1, -1, -1,
-1, 0, 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22,
23, 24, 25, -1, -1, -1, -1, -1,
-1, 26, 27, 28, 29, 30, 31, 32,
33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48,
49, 50, 51, -1, -1, -1, -1, -1,
}
encode :: proc(data: []byte, ENC_TBL := ENC_TABLE, allocator := context.allocator) -> (encoded: string, err: mem.Allocator_Error) #optional_allocator_error {
out_length := encoded_len(data)
if out_length == 0 {
return
}
out := strings.builder_make(0, out_length, allocator) or_return
ioerr := encode_into(strings.to_stream(&out), data, ENC_TBL)
assert(ioerr == nil, "string builder should not IO error")
assert(strings.builder_cap(out) == out_length, "buffer resized, `encoded_len` was wrong")
return strings.to_string(out), nil
}
encode_into :: proc(w: io.Writer, data: []byte, ENC_TBL := ENC_TABLE) -> io.Error {
length := len(data)
if length == 0 {
return nil
}
c0, c1, c2, block: int
out: [4]byte
for i := 0; i < length; i += 3 {
#no_bounds_check {
c0, c1, c2 = int(data[i]), -1, -1
if i + 1 < length { c1 = int(data[i + 1]) }
if i + 2 < length { c2 = int(data[i + 2]) }
block = (c0 << 16) | (max(c1, 0) << 8) | max(c2, 0)
out[0] = ENC_TBL[block >> 18 & 63]
out[1] = ENC_TBL[block >> 12 & 63]
out[2] = c1 == -1 ? PADDING : ENC_TBL[block >> 6 & 63]
out[3] = c2 == -1 ? PADDING : ENC_TBL[block & 63]
}
io.write_full(w, out[:]) or_return
}
return nil
}
encoded_len :: proc(data: []byte) -> int {
length := len(data)
if length == 0 {
return 0
}
return ((4 * length / 3) + 3) &~ 3
}
decode :: proc(data: string, DEC_TBL := DEC_TABLE, allocator := context.allocator) -> (decoded: []byte, err: mem.Allocator_Error) #optional_allocator_error {
out_length := decoded_len(data)
out := strings.builder_make(0, out_length, allocator) or_return
ioerr := decode_into(strings.to_stream(&out), data, DEC_TBL)
assert(ioerr == nil, "string builder should not IO error")
assert(strings.builder_cap(out) == out_length, "buffer resized, `decoded_len` was wrong")
return out.buf[:], nil
}
decode_into :: proc(w: io.Writer, data: string, DEC_TBL := DEC_TABLE) -> io.Error {
length := decoded_len(data)
if length == 0 {
return nil
}
c0, c1, c2, c3: int
b0, b1, b2: int
buf: [3]byte
i, j: int
for ; j + 3 <= length; i, j = i + 4, j + 3 {
#no_bounds_check {
c0 = DEC_TBL[data[i]]
c1 = DEC_TBL[data[i + 1]]
c2 = DEC_TBL[data[i + 2]]
c3 = DEC_TBL[data[i + 3]]
b0 = (c0 << 2) | (c1 >> 4)
b1 = (c1 << 4) | (c2 >> 2)
b2 = (c2 << 6) | c3
buf[0] = byte(b0)
buf[1] = byte(b1)
buf[2] = byte(b2)
}
io.write_full(w, buf[:]) or_return
}
rest := length - j
if rest > 0 {
#no_bounds_check {
c0 = DEC_TBL[data[i]]
c1 = DEC_TBL[data[i + 1]]
c2 = DEC_TBL[data[i + 2]]
b0 = (c0 << 2) | (c1 >> 4)
b1 = (c1 << 4) | (c2 >> 2)
}
switch rest {
case 1: io.write_byte(w, byte(b0)) or_return
case 2: io.write_full(w, {byte(b0), byte(b1)}) or_return
}
}
return nil
}
decoded_len :: proc(data: string) -> int {
length := len(data)
if length == 0 {
return 0
}
padding: int
if data[length - 1] == PADDING {
if length > 1 && data[length - 2] == PADDING {
padding = 2
} else {
padding = 1
}
}
return ((length * 6) >> 3) - padding
}
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