Faster ll2string() implementation.
Faster ll2string() implementation.

Based on ideas documented in this blog post:

https://www.facebook.com/notes/facebook-engineering/three-optimization-tips-for-c/10151361643253920

The original code was modified to handle signed integers, reformetted to
fit inside the Redis code base, and was stress-tested with a program
in order to validate the implementation against snprintf().

Redis was measured to be measurably faster from the point of view of
clients in real-world operations because of this change, since sometimes
number to string conversion is used extensively (for example every time
a GET results into an integer encoded object to be returned to the
user).

splitice/redis,xuzhezhaozhao/redis_reading,xuzhezhaozhao/redis_reading,darksideofthemoo/redis-histogram,louisliangjun/redis,louisliangjun/redis,xuzhezhaozhao/redis_reading,maodeyi/redis_lua,louisliangjun/redis,MSOpenTech/redis,maodeyi/redis_lua,ramonsnir/redis,ksarch-saas/redis,ttuna/msot-redis,ttuna/msot-redis,darksideofthemoo/redis-histogram,jxwr/redis,HunanTV/redis,ksarch-saas/redis,slfs007/mk-redis,louisliangjun/redis,splitice/redis,ramonsnir/redis,himoca/redis,MSOpenTech/redis,ramonsnir/redis,jxwr/redis,ksarch-saas/redis,darksideofthemoo/redis-histogram,spearhead-ea/redis,ttuna/msot-redis,ttuna/msot-redis,HunanTV/redis,maodeyi/redis_lua,ksarch-saas/redis,MSOpenTech/redis,ttuna/msot-redis,splitice/redis,himoca/redis,xuzhezhaozhao/redis_reading,splitice/redis,spearhead-ea/redis,jxwr/redis,HunanTV/redis,slfs007/mk-redis,MSOpenTech/redis,himoca/redis,darksideofthemoo/redis-histogram,slfs007/mk-redis,MSOpenTech/redis,spearhead-ea/redis,HunanTV/redis