py/vstr: Change allocation policy, +16 to requested size, instead of *2.
Effect measured on esp8266 port:
Before:
>>> pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44214 ms
This machine benchmarks at 226 pystones/second
>>> pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44246 ms
This machine benchmarks at 226 pystones/second
After:
>>> pystone_lowmem.main(10000)
Pystone(1.2) time for 10000 passes = 44343ms
This machine benchmarks at 225 pystones/second
>>> 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
index f558e3f..cf10f84 100644
--- a/py/vstr.c
+++ b/py/vstr.c
@@ -151,7 +151,7 @@
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;