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// SPDX-License-Identifier: MPL-2.0
// (c) Hare authors <https://harelang.org>
// Encodes a rune as UTF-8 and returns the result as a slice. The return value
// is statically allocated, and will not be consistent after subsequent calls to
// encoderune.
export fn encoderune(r: rune) []u8 = {
let ch = r: u32, n = 0z, first = 0u8;
assert((ch < 0xD800 || ch > 0xDFFF) && ch <= 0x10FFFF,
"the rune is not a valid Unicode codepoint");
if (ch < 0x80) {
first = 0;
n = 1;
} else if (ch < 0x800) {
first = 0xC0;
n = 2;
} else if (ch < 0x10000) {
first = 0xE0;
n = 3;
} else {
first = 0xF0;
n = 4;
};
static let buf: [4]u8 = [0...];
for (let i = n - 1; i > 0; i -= 1) {
buf[i] = ch: u8 & 0x3F | 0x80;
ch >>= 6;
};
buf[0] = ch: u8 | first;
return buf[..n];
};
@test fn encode() void = {
const expected: [_][]u8 = [
[0],
[0x25],
[0xE3, 0x81, 0x93],
];
const inputs = ['\0', '%', 'こ'];
for (let i = 0z; i < len(inputs); i += 1) {
const out = encoderune(inputs[i]);
for (let j = 0z; j < len(expected[i]); j += 1) {
assert(out[j] == expected[i][j]);
};
};
};
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