Initial project import

tools/v/vlib/crypto/rand/utils.v

@@ -0,0 +1,95 @@
+// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module rand
+
+import math.bits
+import math.big
+import encoding.binary
+
+// int_u64 returns a random unsigned 64-bit integer `u64` read from a real OS source of entropy.
+pub fn int_u64(max u64) !u64 {
+	bitlen := bits.len_64(max)
+	if bitlen == 0 {
+		return u64(0)
+	}
+	k := (bitlen + 7) / 8
+	mut b := u64(bitlen % 8)
+	if b == u64(0) {
+		b = u64(8)
+	}
+	mut n := u64(0)
+	for {
+		mut buf := read(k)!
+		buf[0] &= u8(int(u64(1) << b) - 1)
+		x := bytes_to_u64(buf)
+		n = x[0]
+		// NOTE: maybe until we have bigint could do it another way?
+		// if x.len > 1 {
+		// 	n = u64(u32(x[1])<<u32(32)) | n
+		// }
+		if n < max {
+			return n
+		}
+	}
+	return n
+}
+
+fn bytes_to_u64(b []u8) []u64 {
+	ws := 64 / 8
+	mut z := []u64{len: ((b.len + ws - 1) / ws)}
+	mut i := b.len
+	for k := 0; i >= ws; k++ {
+		z[k] = binary.big_endian_u64(b[i - ws..i])
+		i -= ws
+	}
+	if i > 0 {
+		mut d := u64(0)
+		for s := u64(0); i > 0; s += u64(8) {
+			d |= u64(b[i - 1]) << s
+			i--
+		}
+		z[z.len - 1] = d
+	}
+	return z
+}
+
+// int_big creates a random `big.Integer` with range [0, n)
+// returns an error if `n` is 0 or negative.
+pub fn int_big(n big.Integer) !big.Integer {
+	if n.signum < 1 {
+		return error('`n` cannot be 0 or negative.')
+	}
+
+	max := n - big.integer_from_int(1)
+	len := max.bit_len()
+
+	if len == 0 {
+		// max = n - 1, if max = 0 then return max, as it is the only valid integer in [0, 1)
+		return max
+	}
+
+	// k is the maximum byte length needed to encode a value < n
+	k := (len + 7) / 8
+
+	// b is the number of bits in the most significant byte of n-1
+	mut b := u8(len % 8)
+	if b == 0 {
+		b = 8
+	}
+
+	mut result := big.Integer{}
+	for {
+		mut buf := read(k)!
+
+		// Clear bits in the first byte to increase the probability that the result is < max
+		buf[0] &= u8(int(1 << b) - 1)
+
+		result = big.integer_from_bytes(buf)
+		if result < max {
+			break
+		}
+	}
+	return result
+}