speed improvement for bs58.encode()

[RainaBatwing]

With this change, bs58.encode with 32-digit input runs in about 80% the time the previous version took.

[jprichardson]

It'd be nice to see actual numbers, but I'd imagine that you're probably right with most modern JITs.

[RainaBatwing]

Thank you for accepting my pull! I'm glad I could contribute. Here are the actual numbers from my little old laptop:

$ coffee bench.coffee
bs58: 1672ms
bs58o: 1394ms
bs58: 1667ms
bs58o: 1395ms

bench.coffee is below. I had my modified version of the library in ./node_modules/bs58-0 and the then current version in ./node_modules/bs58. The script repeats the test a few times to try and get V8 nice and warmed up. The results seem pretty consistent. I tried a few different ways of building the string, including preallocating arrays and things, but this was the quickest!

bs58 = require './node_modules/bs58'
bs58o = require './node_modules/bs58-o'

cycles = 50000
# create test input - 32 bytes
test = (x for x in [0..32])

# warm up the code paths in V8
for i in [0...10000]
  bs58.encode(test)
  bs58o.encode(test)

bs58r = null
bs58or = null
console.time('bs58')
for i in [0...cycles]
  bs58r = bs58.encode(test)
console.timeEnd('bs58')

console.time('bs58o')
for i in [0...cycles]
  bs58or = bs58o.encode(test)
console.timeEnd('bs58o')

console.time('bs58')
for i in [0...cycles]
  bs58r = bs58.encode(test)
console.timeEnd('bs58')

console.time('bs58o')
for i in [0...cycles]
  bs58or = bs58o.encode(test)
console.timeEnd('bs58o')

if bs58r != bs58or
  console.log("outputs do not match!", bs58r, bs58or)