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Merge pull request #6202 from roc-lang/substring-slices

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Create seamless slices when getting a substring
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Richard Feldman 2023-12-06 14:31:01 -05:00 • committed by GitHub
commit 6f0857d7da
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3 changed files with 31 additions and 4 deletions
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31
crates/compiler/builtins/bitcode/src/str.zig
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@ -1498,8 +1498,35 @@ pub fn getCapacity(string: RocStr) callconv(.C) usize {
}
pub fn substringUnsafe(string: RocStr, start: usize, length: usize) callconv(.C) RocStr {
const slice = string.asSlice()[start .. start + length];
return RocStr.fromSlice(slice);
if (string.isSmallStr()) {
if (start == 0) {
var output = string;
output.setLen(length);
return output;
}
const slice = string.asSlice()[start .. start + length];
return RocStr.fromSlice(slice);
}
if (string.str_bytes) |source_ptr| {
if (start == 0 and string.isUnique()) {
var output = string;
output.setLen(length);
return output;
} else {
// Shifting right by 1 is required to avoid the highest bit of capacity being set.
// If it was set, the slice would get interpreted as a small string.
const str_ref_ptr = (@intFromPtr(source_ptr) >> 1);
const slice_ref_ptr = string.str_capacity;
const slice_mask = string.seamlessSliceMask();
const ref_ptr = (str_ref_ptr & ~slice_mask) | (slice_ref_ptr & slice_mask);
return RocStr{
.str_bytes = source_ptr + start,
.str_len = length | SEAMLESS_SLICE_BIT,
.str_capacity = ref_ptr,
};
}
}
return RocStr.empty();
}
pub fn getUnsafe(string: RocStr, index: usize) callconv(.C) u8 {