From a3f589640fd443deea230c27efd6bdfc92f5817f Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Wed, 4 Sep 2024 12:38:30 +0200
Subject: [PATCH] Time#strftime: grow the buffer faster

Use a classic doubling of capacity rather than only adding
twice as much capacity as is already known to be needed.

```
compare-ruby: ruby 3.4.0dev (2024-09-04T09:21:53Z opt-strftime-2 ae98d19cf9) +YJIT [arm64-darwin23]
built-ruby: ruby 3.4.0dev (2024-09-04T11:46:02Z opt-strftime-growth 586263d6fb) +YJIT [arm64-darwin23]
warming up...

|                            |compare-ruby|built-ruby|
|:---------------------------|-----------:|---------:|
|time.strftime("%FT%T")      |      1.754M|    1.889M|
|                            |           -|     1.08x|
|time.strftime("%FT%T.%3N")  |      1.508M|    1.749M|
|                            |           -|     1.16x|
|time.strftime("%FT%T.%6N")  |      1.488M|    1.756M|
|                            |           -|     1.18x|
compare-ruby: ruby 3.4.0dev (2024-09-04T09:21:53Z opt-strftime-2 ae98d19cf9) +YJIT [arm64-darwin23]
built-ruby: ruby 3.4.0dev (2024-09-04T09:21:53Z opt-strftime-2 ae98d19cf9) +YJIT [arm64-darwin23]
warming up...
```
---
 benchmark/time_strftime.yml | 7 +++++++
 strftime.c                  | 4 +++-
 2 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 benchmark/time_strftime.yml

diff --git a/benchmark/time_strftime.yml b/benchmark/time_strftime.yml
new file mode 100644
index 0000000000..28f62aec87
--- /dev/null
+++ b/benchmark/time_strftime.yml
@@ -0,0 +1,7 @@
+prelude: |
+  # frozen_string_literal: true
+  time = Time.now
+benchmark:
+  - time.strftime("%FT%T")     # 19B
+  - time.strftime("%FT%T.%3N") # 23B
+  - time.strftime("%FT%T.%6N") # 26B
diff --git a/strftime.c b/strftime.c
index 33e7d3fdb8..906e8360a9 100644
--- a/strftime.c
+++ b/strftime.c
@@ -171,7 +171,9 @@ resize_buffer(VALUE ftime, char *s, const char **start, const char **endp,
 	      ptrdiff_t n, size_t maxsize)
 {
 	size_t len = s - *start;
-	size_t nlen = len + n * 2;
+	size_t need = len + n * 2;
+	size_t nlen = rb_str_capacity(ftime);
+	while (nlen < need) nlen <<= 1;
 
 	if (nlen < len || nlen > maxsize) {
 		return 0;