strconv: Avoid allocation in AppendQuote*
The current implementations of the AppendQuote functions use quoteWith (through Quote) for quoting the given value and appends the returned string to the dst byte slice. quoteWith internally creates a byte slice on each call which gets converted to a string in Quote. This means the AppendQuote functions always allocates a new byte slice and a string only to append them to an existing byte slice. In the case of (Append)QuoteRune the string passed to quoteWith will also needs to be allocated from a rune first. Split quoteWith into two functions (quoteWith and appendQuotedWith) and replace the call to Quote inside AppendQuote with appendQuotedWith, which appends directly to the byte slice passed to AppendQuote and also avoids the []byte->string conversion. Also introduce the 2 functions quoteRuneWith and appendQuotedRuneWith that work the same way as quoteWith and appendQuotedWith, but take a single rune instead of a string, to avoid allocating a new string when appending a single rune, and use them in (Append)QuoteRune. Also update the ToASCII and ToGraphic variants to use the new functions. Benchmark results: benchmark old ns/op new ns/op delta BenchmarkQuote-8 428 503 +17.52% BenchmarkQuoteRune-8 148 105 -29.05% BenchmarkAppendQuote-8 435 307 -29.43% BenchmarkAppendQuoteRune-8 158 23.5 -85.13% benchmark old allocs new allocs delta BenchmarkQuote-8 3 3 +0.00% BenchmarkQuoteRune-8 3 2 -33.33% BenchmarkAppendQuote-8 3 0 -100.00% BenchmarkAppendQuoteRune-8 3 0 -100.00% benchmark old bytes new bytes delta BenchmarkQuote-8 144 144 +0.00% BenchmarkQuoteRune-8 16 16 +0.00% BenchmarkAppendQuote-8 144 0 -100.00% BenchmarkAppendQuoteRune-8 16 0 -100.00% Change-Id: I77c148d5c7242f1b0edbbeeea184878abb51a522 Reviewed-on: https://go-review.googlesource.com/18962 Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
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