encoding: add base58 support (#11288)

vlib/encoding/base58/base58.v

@@ -0,0 +1,181 @@
+// algorthim is adapted from https://github.com/mr-tron/base58 under the MIT license
+
+module base58
+
+import math
+
+// encode_int encodes any integer type to base58 string with Bitcoin alphabet
+pub fn encode_int(input int) ?string {
+	return encode_int_walpha(input, alphabets['btc'])
+}
+
+// encode_int_walpha any integer type to base58 string with custom alphabet
+pub fn encode_int_walpha(input int, alphabet Alphabet) ?string {
+	if input <= 0 {
+		return error(@MOD + '.' + @FN + ': input must be greater than zero')
+	}
+
+	mut buffer := []byte{}
+
+	mut i := input
+	for i > 0 {
+		remainder := i % 58
+		buffer << alphabet.encode[i8(remainder)]
+		// This needs to be casted so byte inputs can
+		// be used. i8 because remainder will never be
+		// over 58.
+		i = i / 58
+	}
+
+	return buffer.reverse().bytestr()
+}
+
+// encode encodes byte array to base58 with Bitcoin alphabet
+pub fn encode(input string) string {
+	return encode_walpha(input, alphabets['btc'])
+}
+
+// encode_walpha encodes byte array to base58 with custom aplhabet
+pub fn encode_walpha(input string, alphabet Alphabet) string {
+	if input.len == 0 {
+		return ''
+	}
+
+	bin := input.bytes()
+	mut sz := bin.len
+
+	mut zcount := 0
+	for zcount < sz && bin[zcount] == 0 {
+		zcount++
+	}
+
+	// It is crucial to make this as short as possible, especially for
+	// the usual case of Bitcoin addresses
+	sz = zcount + (sz - zcount) * 555 / 406 + 1
+	// integer simplification of
+	// ceil(log(256)/log(58))
+
+	mut out := []byte{len: sz}
+	mut i := 0
+	mut high := 0
+	mut carry := u32(0)
+
+	high = sz - 1
+	for b in bin {
+		i = sz - 1
+		for carry = u32(b); i > high || carry != 0; i-- {
+			carry = carry + 256 * u32(out[i])
+			out[i] = byte(carry % 58)
+			carry /= 58
+		}
+		high = 1
+	}
+
+	// determine additional "zero-gap" in the buffer, aside from zcount
+	for i = zcount; i < sz && out[i] == 0; i++ {}
+
+	// now encode the values with actual alphabet in-place
+	val := out[i - zcount..]
+	sz = val.len
+	for i = 0; i < sz; i++ {
+		out[i] = alphabet.encode[val[i]]
+	}
+
+	return out[..sz].bytestr()
+}
+
+// decode_int decodes base58 string to an integer with Bitcoin alphabet
+pub fn decode_int(input string) ?int {
+	return decode_int_walpha(input, alphabets['btc'])
+}
+
+// decode_int_walpha decodes base58 string to an integer with custom alphabet
+pub fn decode_int_walpha(input string, alphabet Alphabet) ?int {
+	mut total := 0 // to hold the results
+	b58 := input.reverse()
+	for i, ch in b58 {
+		ch_i := alphabet.encode.bytestr().index_byte(ch)
+		if ch_i == -1 {
+			return error(@MOD + '.' + @FN +
+				': input string contains values not found in the provided alphabet')
+		}
+
+		val := ch_i * math.pow(58, i)
+
+		total += int(val)
+	}
+
+	return total
+}
+
+// decode decodes base58 string using the Bitcoin alphabet
+pub fn decode(str string) ?string {
+	return decode_walpha(str, alphabets['btc'])
+}
+
+// decode_walpha decodes base58 string using custom alphabet
+pub fn decode_walpha(str string, alphabet Alphabet) ?string {
+	if str.len == 0 {
+		return ''
+	}
+
+	zero := alphabet.encode[0]
+	b58sz := str.len
+
+	mut zcount := 0
+	for i := 0; i < b58sz && str[i] == zero; i++ {
+		zcount++
+	}
+
+	mut t := u64(0)
+	mut c := u64(0)
+
+	// the 32-bit algorithm stretches the result up to 2x
+	mut binu := []byte{len: 2 * ((b58sz * 406 / 555) + 1)}
+	mut outi := []u32{len: (b58sz + 3) / 4}
+
+	for _, r in str {
+		if r > 127 {
+			panic(@MOD + '.' + @FN +
+				': high-bit set on invalid digit; outside of ascii range ($r). This should never happen.')
+		}
+		if alphabet.decode[r] == -1 {
+			return error(@MOD + '.' + @FN + ': invalid base58 digit ($r)')
+		}
+
+		c = u64(alphabet.decode[r])
+
+		for j := outi.len - 1; j >= 0; j-- {
+			t = u64(outi[j]) * 58 + c
+			c = t >> 32
+			outi[j] = u32(t & 0xffffffff)
+		}
+	}
+
+	// initial mask depend on b58sz, on further loops it always starts at 24 bits
+	mut mask := (u32(b58sz % 4) * 8)
+	if mask == 0 {
+		mask = 32
+	}
+	mask -= 8
+
+	mut out_len := 0
+	for j := 0; j < outi.len; j++ {
+		for mask < 32 {
+			binu[out_len] = byte(outi[j] >> mask)
+			mask -= 8
+			out_len++
+		}
+		mask = 24
+	}
+
+	// find the most significant byte post-decode, if any
+	for msb := zcount; msb < binu.len; msb++ { // loop relies on u32 overflow
+		if binu[msb] > 0 {
+			return binu[msb - zcount..out_len].bytestr()
+		}
+	}
+
+	// it's all zeroes
+	return binu[..out_len].bytestr()
+}