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| function con(b) { | |
| if ((b & 0xc0) === 0x80) { | |
| return b & 0x3f; | |
| } else { | |
| throw new Error("invalid UTF-8 encoding"); | |
| } | |
| } | |
| function code(min, n) { | |
| if (n < min || (0xd800 <= n && n < 0xe000) || n >= 0x10000) { | |
| throw new Error("invalid UTF-8 encoding"); | |
| } else { | |
| return n; | |
| } | |
| } | |
| export function decode(bytes) { | |
| return _decode(bytes) | |
| .map(x => String.fromCharCode(x)) | |
| .join(""); | |
| } | |
| function _decode(bytes) { | |
| if (bytes.length === 0) { | |
| return []; | |
| } | |
| /** | |
| * 1 byte | |
| */ | |
| { | |
| const [b1, ...bs] = bytes; | |
| if (b1 < 0x80) { | |
| return [code(0x0, b1), ..._decode(bs)]; | |
| } | |
| if (b1 < 0xc0) { | |
| throw new Error("invalid UTF-8 encoding"); | |
| } | |
| } | |
| /** | |
| * 2 bytes | |
| */ | |
| { | |
| const [b1, b2, ...bs] = bytes; | |
| if (b1 < 0xe0) { | |
| return [code(0x80, ((b1 & 0x1f) << 6) + con(b2)), ..._decode(bs)]; | |
| } | |
| } | |
| /** | |
| * 3 bytes | |
| */ | |
| { | |
| const [b1, b2, b3, ...bs] = bytes; | |
| if (b1 < 0xf0) { | |
| return [ | |
| code(0x800, ((b1 & 0x0f) << 12) + (con(b2) << 6) + con(b3)), | |
| ..._decode(bs) | |
| ]; | |
| } | |
| } | |
| /** | |
| * 4 bytes | |
| */ | |
| { | |
| const [b1, b2, b3, b4, ...bs] = bytes; | |
| if (b1 < 0xf8) { | |
| return [ | |
| code( | |
| 0x10000, | |
| ((((b1 & 0x07) << 18) + con(b2)) << 12) + (con(b3) << 6) + con(b4) | |
| ), | |
| ..._decode(bs) | |
| ]; | |
| } | |
| } | |
| throw new Error("invalid UTF-8 encoding"); | |
| } | |