rand: add `pub fn rand.read(mut buf []byte)` and `pub fn rand.bytes(needed int) ?[]byte{}` + tests

vlib/rand/rand.c.v

@@ -138,3 +138,17 @@ fn init() {
 	default_rng = new_default()
 	C.atexit(deinit)
 }
+
+// read fills in `buf` a maximum of `buf.len` random bytes
+pub fn read(mut buf []byte) {
+	p64 := unsafe { &u64(buf.data) }
+	u64s := buf.len / 8
+	for i in 0 .. u64s {
+		unsafe {
+			*(p64 + i) = default_rng.u64()
+		}
+	}
+	for i in u64s * 8 .. buf.len {
+		buf[i] = byte(default_rng.u32())
+	}
+}

vlib/rand/rand.js.v

@@ -65,3 +65,10 @@ pub fn ulid_at_millisecond(unix_time_milli u64) string {
 
 	return res
 }
+
+// read fills in `buf` a maximum of `buf.len` random bytes
+pub fn read(mut buf []byte) {
+	for i in 0 .. buf.len {
+		buf[i] = byte(default_rng.u32())
+	}
+}

vlib/rand/rand.v

@@ -174,6 +174,16 @@ pub fn f64_in_range(min f64, max f64) f64 {
 	return default_rng.f64_in_range(min, max)
 }
 
+// bytes returns a buffer of `bytes_needed` random bytes
+pub fn bytes(bytes_needed int) ?[]byte {
+	if bytes_needed < 0 {
+		return error('can not read < 0 random bytes')
+	}
+	mut res := []byte{len: bytes_needed}
+	read(mut res)
+	return res
+}
+
 const (
 	english_letters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
 	hex_chars       = 'abcdef0123456789'

vlib/rand/random_bytes_test.v

@@ -0,0 +1,51 @@
+import rand
+
+fn test_rand_bytes() ? {
+	mut randoms := []string{}
+	for i in 0 .. 100 {
+		x := rand.bytes(i) ?.hex()
+		if x.len > 0 {
+			randoms << x
+		}
+		assert x.len == i * 2
+	}
+	mut differences := 0
+	for idx in 1 .. randoms.len {
+		start := randoms[idx]#[0..8]
+		prev_start := randoms[idx - 1]#[0..8]
+		if start != prev_start {
+			differences++
+		}
+	}
+	assert differences > 95 // normally around 98
+	dump(differences)
+}
+
+fn test_rand_read() ? {
+	max := 50
+	mut a := []byte{len: max}
+	mut differences := 0
+	for j in 1 .. max {
+		start := '00'.repeat(j)
+		for k in j + 1 .. max {
+			end := '00'.repeat(max - k)
+			middle := '00'.repeat(k - j)
+			// eprintln('> j: $j | k: $k | start: $start | middle: $middle | end: $end')
+			for i in 0 .. max {
+				a[i] = 0
+			}
+			assert a[j..k].hex() == middle
+			for i in 0 .. 10 {
+				rand.read(mut a[j..k])
+				// dump(a.hex())
+				assert a[0..j].hex() == start
+				assert a[k..].hex() == end
+				if a[j..k].hex() != middle {
+					differences++
+				}
+			}
+		}
+	}
+	dump(differences)
+	assert differences > 11700 // normally around 11758
+}