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Optimise encodeInto reallocations

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Instead of doubling the size on each iteration, use precise upper limit (3 * JS length) if the string turned out not to be ASCII-only. This results in maximum of 1 reallocation instead of O(log N).

Some dummy examples of what this would change:
 - 1000 of ASCII chars: no change, allocates 1000 bytes and bails out.
 - 1000 ASCII chars + 1 '😃': before allocated 1000 bytes and reallocated to 2000; now allocates 1000 bytes and reallocates to 1006.
 - 1000 of '😃' chars: before allocated 1000 bytes, reallocated to 2000, finally reallocated again to 4000; now allocates 1000 bytes and reallocates to 4000 right away.

Related issue: #1313
This commit is contained in:
Ingvar Stepanyan
2019-04-01 13:08:08 +01:00
parent 1121393203
commit 2f28b8b80e
1 changed files with 4 additions and 5 deletions
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9
crates/cli-support/src/js/mod.rs
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@ -1306,13 +1306,12 @@ impl<'a> Context<'a> {
while (true) {{
const view = getUint8Memory().subarray(ptr + writeOffset, ptr + size);
const {{ read, written }} = cachedTextEncoder.encodeInto(arg, view);
arg = arg.substring(read);
writeOffset += written;
if (arg.length === 0) {{
if (read === arg.length) {{
break;
}}
ptr = wasm.__wbindgen_realloc(ptr, size, size * 2);
size *= 2;
arg = arg.substring(read);
writeOffset += written;
ptr = wasm.__wbindgen_realloc(ptr, size, size += arg.length * 3);
}}
WASM_VECTOR_LEN = writeOffset;
return ptr;