From 732d8101e07326c93a6010fdaa3490809ce3b5fb Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Mon, 19 Jul 2021 16:42:37 +0300
Subject: [PATCH] math.big: add .bytes() and .bytes_trimmed() methods,
 `big.from_int(1024).bytes_trimmed() == [byte(0x00), 0x04]`

---
 vlib/math/big/big.v      | 34 ++++++++++++++++++++++++++++++++++
 vlib/math/big/big_test.v | 22 ++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/vlib/math/big/big.v b/vlib/math/big/big.v
index 0bbb5717d9..00658c799c 100644
--- a/vlib/math/big/big.v
+++ b/vlib/math/big/big.v
@@ -282,3 +282,37 @@ pub fn factorial(nn Number) Number {
 pub fn fact(n int) Number {
 	return factorial(from_int(n))
 }
+
+// bytes returns an array of the bytes for the number `n`,
+// in little endian format, where .bytes()[0] is the least
+// significant byte. The result is NOT trimmed, and will contain 0s, even
+// after the significant bytes.
+// This method is faster than .bytes_trimmed(), but may be less convenient.
+// Example: assert big.from_int(1).bytes()[0] == byte(0x01)
+// Example: assert big.from_int(1024).bytes()[1] == byte(0x04)
+// Example: assert big.from_int(1048576).bytes()[2] == byte(0x10)
+pub fn (n &Number) bytes() []byte {
+	mut res := []byte{len: 128, init: 0}
+	unsafe { C.memcpy(res.data, n, 128) }
+	return res
+}
+
+// bytes_trimmed returns an array of the bytes for the number `n`,
+// in little endian format, where .bytes_trimmed()[0] is the least
+// significant byte. The result is trimmed, so that *the last* byte
+// of the result is also the the last meaningfull byte, != 0 .
+// Example: assert big.from_int(1).bytes_trimmed() == [byte(0x01)]
+// Example: assert big.from_int(1024).bytes_trimmed() == [byte(0x00), 0x04]
+// Example: assert big.from_int(1048576).bytes_trimmed() == [byte(0x00), 0x00, 0x10]
+pub fn (n &Number) bytes_trimmed() []byte {
+	mut res := []byte{len: 128, init: 0}
+	unsafe { C.memcpy(res.data, n, 128) }
+	mut non_zero_idx := 127
+	for ; non_zero_idx >= 0; non_zero_idx-- {
+		if res[non_zero_idx] != 0 {
+			break
+		}
+	}
+	res.trim(non_zero_idx + 1)
+	return res
+}
diff --git a/vlib/math/big/big_test.v b/vlib/math/big/big_test.v
index 6ba78686ed..63982cadcc 100644
--- a/vlib/math/big/big_test.v
+++ b/vlib/math/big/big_test.v
@@ -126,3 +126,25 @@ fn test_factorial() {
 	f100 := big.factorial(big.from_u64(100))
 	assert f100.hexstr() == '1b30964ec395dc24069528d54bbda40d16e966ef9a70eb21b5b2943a321cdf10391745570cca9420c6ecb3b72ed2ee8b02ea2735c61a000000000000000000000000'
 }
+
+fn trimbytes(n int, x []byte) []byte {
+	mut res := x.clone()
+	res.trim(n)
+	return res
+}
+
+fn test_bytes() {
+	assert big.from_int(0).bytes().len == 128
+	assert big.from_hex_string('e'.repeat(100)).bytes().len == 128
+	assert trimbytes(3, big.from_int(1).bytes()) == [byte(0x01), 0x00, 0x00]
+	assert trimbytes(3, big.from_int(1024).bytes()) == [byte(0x00), 0x04, 0x00]
+	assert trimbytes(3, big.from_int(1048576).bytes()) == [byte(0x00), 0x00, 0x10]
+}
+
+fn test_bytes_trimmed() {
+	assert big.from_int(0).bytes_trimmed().len == 0
+	assert big.from_hex_string('AB'.repeat(50)).bytes_trimmed().len == 50
+	assert big.from_int(1).bytes_trimmed() == [byte(0x01)]
+	assert big.from_int(1024).bytes_trimmed() == [byte(0x00), 0x04]
+	assert big.from_int(1048576).bytes_trimmed() == [byte(0x00), 0x00, 0x10]
+}