common: move big integer math to common/math (#3699)

* common: remove CurrencyToString

Move denomination values to params instead.

* common: delete dead code

* common: move big integer operations to common/math

This commit consolidates all big integer operations into common/math and
adds tests and documentation.

There should be no change in semantics for BigPow, BigMin, BigMax, S256,
U256, Exp and their behaviour is now locked in by tests.

The BigD, BytesToBig and Bytes2Big functions don't provide additional
value, all uses are replaced by new(big.Int).SetBytes().

BigToBytes is now called PaddedBigBytes, its minimum output size
parameter is now specified as the number of bytes instead of bits. The
single use of this function is in the EVM's MSTORE instruction.

Big and String2Big are replaced by ParseBig, which is slightly stricter.
It previously accepted leading zeros for hexadecimal inputs but treated
decimal inputs as octal if a leading zero digit was present.

ParseUint64 is used in places where String2Big was used to decode a
uint64.

The new functions MustParseBig and MustParseUint64 are now used in many
places where parsing errors were previously ignored.

* common: delete unused big integer variables

* accounts/abi: replace uses of BytesToBig with use of encoding/binary

* common: remove BytesToBig

* common: remove Bytes2Big

* common: remove BigTrue

* cmd/utils: add BigFlag and use it for error-checked integer flags

While here, remove environment variable processing for DirectoryFlag
because we don't use it.

* core: add missing error checks in genesis block parser

* common: remove String2Big

* cmd/evm: use utils.BigFlag

* common/math: check for 256 bit overflow in ParseBig

This is supposed to prevent silent overflow/truncation of values in the
genesis block JSON. Without this check, a genesis block that set a
balance larger than 256 bits would lead to weird behaviour in the VM.

* cmd/utils: fixup import

1 files changed, 0 insertions, 140 deletions

diff --git a/common/README.md b/common/README.md
deleted file mode 100644
index adea022b7..000000000
--- a/common/README.md
+++ /dev/null
@@ -1,140 +0,0 @@
-# common
-
-[![Build
-Status](https://travis-ci.org/ethereum/go-ethereum.png?branch=master)](https://travis-ci.org/ethereum/go-ethereum)
-
-The common package contains the ethereum utility library.
-
-# Installation
-
-As a subdirectory the main go-ethereum repository, you get it with
-`go get github.com/ethereum/go-ethereum`.
-
-# Usage
-
-## RLP (Recursive Linear Prefix) Encoding
-
-RLP Encoding is an encoding scheme used by the Ethereum project. It
-encodes any native value or list to a string.
-
-More in depth information about the encoding scheme see the
-[Wiki](http://wiki.ethereum.org/index.php/RLP) article.
-
-```go
-rlp := common.Encode("doge")
-fmt.Printf("%q\n", rlp) // => "\0x83dog"
-
-rlp = common.Encode([]interface{}{"dog", "cat"})
-fmt.Printf("%q\n", rlp) // => "\0xc8\0x83dog\0x83cat"
-decoded := common.Decode(rlp)
-fmt.Println(decoded) // => ["dog" "cat"]
-```
-
-## Patricia Trie
-
-Patricie Tree is a merkle trie used by the Ethereum project.
-
-More in depth information about the (modified) Patricia Trie can be
-found on the [Wiki](http://wiki.ethereum.org/index.php/Patricia_Tree).
-
-The patricia trie uses a db as backend and could be anything as long as
-it satisfies the Database interface found in `common/db.go`.
-
-```go
-db := NewDatabase()
-
-// db, root
-trie := common.NewTrie(db, "")
-
-trie.Put("puppy", "dog")
-trie.Put("horse", "stallion")
-trie.Put("do", "verb")
-trie.Put("doge", "coin")
-
-// Look up the key "do" in the trie
-out := trie.Get("do")
-fmt.Println(out) // => verb
-
-trie.Delete("puppy")
-```
-
-The patricia trie, in combination with RLP, provides a robust,
-cryptographically authenticated data structure that can be used to store
-all (key, value) bindings.
-
-```go
-// ... Create db/trie
-
-// Note that RLP uses interface slices as list
-value := common.Encode([]interface{}{"one", 2, "three", []interface{}{42}})
-// Store the RLP encoded value of the list
-trie.Put("mykey", value)
-```
-
-## Value
-
-Value is a Generic Value which is used in combination with RLP data or
-`([])interface{}` structures. It may serve as a bridge between RLP data
-and actual real values and takes care of all the type checking and
-casting. Unlike Go's `reflect.Value` it does not panic if it's unable to
-cast to the requested value. It simple returns the base value of that
-type (e.g. `Slice()` returns []interface{}, `Uint()` return 0, etc).
-
-### Creating a new Value
-
-`NewEmptyValue()` returns a new \*Value with it's initial value set to a
-`[]interface{}`
-
-`AppendList()` appends a list to the current value.
-
-`Append(v)` appends the value (v) to the current value/list.
-
-```go
-val := common.NewEmptyValue().Append(1).Append("2")
-val.AppendList().Append(3)
-```
-
-### Retrieving values
-
-`Get(i)` returns the `i` item in the list.
-
-`Uint()` returns the value as an unsigned int64.
-
-`Slice()` returns the value as a interface slice.
-
-`Str()` returns the value as a string.
-
-`Bytes()` returns the value as a byte slice.
-
-`Len()` assumes current to be a slice and returns its length.
-
-`Byte()` returns the value as a single byte.
-
-```go
-val := common.NewValue([]interface{}{1,"2",[]interface{}{3}})
-val.Get(0).Uint() // => 1
-val.Get(1).Str()  // => "2"
-s := val.Get(2)   // => Value([]interface{}{3})
-s.Get(0).Uint()   // => 3
-```
-
-## Decoding
-
-Decoding streams of RLP data is simplified
-
-```go
-val := common.NewValueFromBytes(rlpData)
-val.Get(0).Uint()
-```
-
-## Encoding
-
-Encoding from Value to RLP is done with the `Encode` method. The
-underlying value can be anything RLP can encode (int, str, lists, bytes)
-
-```go
-val := common.NewValue([]interface{}{1,"2",[]interface{}{3}})
-rlp := val.Encode()
-// Store the rlp data
-Store(rlp)
-```