Refactor Base58 decoding in naka3.sh for ARM large number handling

[moodmosaic]

Resolves #1.

[moodmosaic]

/cc @wileyj

[jcnelson]

This doesn't seem to work for mainnet addresses:

$ cat /tmp/b58.sh
#!/bin/bash

# Decode b58 text into a hex byte stream
# $1: base58 text
# from https://github.com/grondilu/bitcoin-bash-tools
function b58_decode() {
   local base58_chars="123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
   local base58_text="$1"
   local base58_length=${#base58_chars}
   local result="0"
   local i=0
   local char
   local value

   for (( i=0; i<${#base58_text}; i++ )); do
       char="${base58_text:i:1}"
       value=$(expr index "$base58_chars" "$char")
       value=$((value - 1))
       result=$(echo "$result * $base58_length + $value" | bc)
   done

   # Convert the result to hex using bc and xxd without printf
   echo "obase=16; $result" | bc | xxd -r -p | xxd -p
}

# Decode a base58 Bitcoin address into "$version_byte $hash_bytes"
# $1: address
# prints the above
function b58_address_decode() {
   local addr="$1"
   local decoded_hex=$(b58_decode "$addr")
   local version_byte="${decoded_hex:0:2}"
   local hash_bytes="${decoded_hex:2:40}"
   echo "$version_byte $hash_bytes"
}

b58_address_decode "$1"

To see:

$ bash ./b58.sh 1PMycacnJaSqwwJqjawXBErnLsZ7RkXUAs
f5 4a5851e9372b87810a8e60cdd2e7cfd80b6e31c7

It should instead decode to:

$ bash ./b58.sh 1PMycacnJaSqwwJqjawXBErnLsZ7RkXUAs
00 f54a5851e9372b87810a8e60cdd2e7cfd80b6e31c7