py/vstr: Change allocation policy, +16 to requested size, instead of *2.

pfalcon · pfalcon · commit 6f34e138f1ec · 2016-05-10T00:56:51.000+03:00
Effect measured on esp8266 port:

Before:
&gt;&gt;&gt; pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44214 ms
This machine benchmarks at 226 pystones/second
&gt;&gt;&gt; pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44246 ms
This machine benchmarks at 226 pystones/second

After:
&gt;&gt;&gt; pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44343ms
This machine benchmarks at 225 pystones/second
&gt;&gt;&gt; pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44376ms
This machine benchmarks at 225 pystones/second
diff --git a/py/vstr.c b/py/vstr.c
@@ -151,7 +151,7 @@ STATIC bool vstr_ensure_extra(vstr_t *vstr, size_t size) {
         if (vstr->fixed_buf) {
             return false;
         }
-        size_t new_alloc = ROUND_ALLOC((vstr->len + size) * 2);
+        size_t new_alloc = ROUND_ALLOC((vstr->len + size) + 16);
         char *new_buf = m_renew(char, vstr->buf, vstr->alloc, new_alloc);
         if (new_buf == NULL) {
             vstr->had_error = true;

Original file line number	Diff line number	Diff line change
`@@ -151,7 +151,7 @@ STATIC bool vstr_ensure_extra(vstr_t *vstr, size_t size) {`
`151`	`151`	`if (vstr->fixed_buf) {`
`152`	`152`	`return false;`
`153`	`153`	`}`
`154`		`- size_t new_alloc = ROUND_ALLOC((vstr->len + size) * 2);`
	`154`	`+ size_t new_alloc = ROUND_ALLOC((vstr->len + size) + 16);`
`155`	`155`	`char *new_buf = m_renew(char, vstr->buf, vstr->alloc, new_alloc);`
`156`	`156`	`if (new_buf == NULL) {`
`157`	`157`	`vstr->had_error = true;`