std::rand: move the Isaac implementation to its own file.

Author: huonw

src/libstd/rand/isaac.rs

@@ -0,0 +1,198 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! The ISAAC random number generator.
+
+use rand::{seed, Rng};
+use iter::{Iterator, range, range_step};
+use option::{None, Some};
+
+use cast;
+use cmp;
+use sys;
+use vec;
+
+static RAND_SIZE_LEN: u32 = 8;
+static RAND_SIZE: u32 = 1 << RAND_SIZE_LEN;
+
+/// A random number generator that uses the [ISAAC
+/// algorithm](http://en.wikipedia.org/wiki/ISAAC_%28cipher%29).
+///
+/// The ISAAC algorithm is suitable for cryptographic purposes.
+pub struct IsaacRng {
+    priv cnt: u32,
+    priv rsl: [u32, .. RAND_SIZE],
+    priv mem: [u32, .. RAND_SIZE],
+    priv a: u32,
+    priv b: u32,
+    priv c: u32
+}
+
+impl IsaacRng {
+    /// Create an ISAAC random number generator with a random seed.
+    pub fn new() -> IsaacRng {
+        IsaacRng::new_seeded(seed(RAND_SIZE as uint * 4))
+    }
+
+    /// Create an ISAAC random number generator with a seed. This can be any
+    /// length, although the maximum number of bytes used is 1024 and any more
+    /// will be silently ignored. A generator constructed with a given seed
+    /// will generate the same sequence of values as all other generators
+    /// constructed with the same seed.
+    pub fn new_seeded(seed: &[u8]) -> IsaacRng {
+        let mut rng = IsaacRng {
+            cnt: 0,
+            rsl: [0, .. RAND_SIZE],
+            mem: [0, .. RAND_SIZE],
+            a: 0, b: 0, c: 0
+        };
+
+        let array_size = sys::size_of_val(&rng.rsl);
+        let copy_length = cmp::min(array_size, seed.len());
+
+        // manually create a &mut [u8] slice of randrsl to copy into.
+        let dest = unsafe { cast::transmute((&mut rng.rsl, array_size)) };
+        vec::bytes::copy_memory(dest, seed, copy_length);
+        rng.init(true);
+        rng
+    }
+
+    /// Create an ISAAC random number generator using the default
+    /// fixed seed.
+    pub fn new_unseeded() -> IsaacRng {
+        let mut rng = IsaacRng {
+            cnt: 0,
+            rsl: [0, .. RAND_SIZE],
+            mem: [0, .. RAND_SIZE],
+            a: 0, b: 0, c: 0
+        };
+        rng.init(false);
+        rng
+    }
+
+    /// Initialises `self`. If `use_rsl` is true, then use the current value
+    /// of `rsl` as a seed, otherwise construct one algorithmically (not
+    /// randomly).
+    fn init(&mut self, use_rsl: bool) {
+        let mut a = 0x9e3779b9;
+        let mut b = a;
+        let mut c = a;
+        let mut d = a;
+        let mut e = a;
+        let mut f = a;
+        let mut g = a;
+        let mut h = a;
+
+        macro_rules! mix(
+            () => {{
+                a^=b<<11; d+=a; b+=c;
+                b^=c>>2;  e+=b; c+=d;
+                c^=d<<8;  f+=c; d+=e;
+                d^=e>>16; g+=d; e+=f;
+                e^=f<<10; h+=e; f+=g;
+                f^=g>>4;  a+=f; g+=h;
+                g^=h<<8;  b+=g; h+=a;
+                h^=a>>9;  c+=h; a+=b;
+            }}
+        );
+
+        do 4.times { mix!(); }
+
+        if use_rsl {
+            macro_rules! memloop (
+                ($arr:expr) => {{
+                    for i in range_step(0u32, RAND_SIZE, 8) {
+                        a+=$arr[i  ]; b+=$arr[i+1];
+                        c+=$arr[i+2]; d+=$arr[i+3];
+                        e+=$arr[i+4]; f+=$arr[i+5];
+                        g+=$arr[i+6]; h+=$arr[i+7];
+                        mix!();
+                        self.mem[i  ]=a; self.mem[i+1]=b;
+                        self.mem[i+2]=c; self.mem[i+3]=d;
+                        self.mem[i+4]=e; self.mem[i+5]=f;
+                        self.mem[i+6]=g; self.mem[i+7]=h;
+                    }
+                }}
+            );
+
+            memloop!(self.rsl);
+            memloop!(self.mem);
+        } else {
+            for i in range_step(0u32, RAND_SIZE, 8) {
+                mix!();
+                self.mem[i  ]=a; self.mem[i+1]=b;
+                self.mem[i+2]=c; self.mem[i+3]=d;
+                self.mem[i+4]=e; self.mem[i+5]=f;
+                self.mem[i+6]=g; self.mem[i+7]=h;
+            }
+        }
+
+        self.isaac();
+    }
+
+    /// Refills the output buffer (`self.rsl`)
+    #[inline]
+    fn isaac(&mut self) {
+        self.c += 1;
+        // abbreviations
+        let mut a = self.a;
+        let mut b = self.b + self.c;
+
+        static MIDPOINT: uint = RAND_SIZE as uint / 2;
+
+        macro_rules! ind (($x:expr) => {
+            self.mem[($x >> 2) & (RAND_SIZE - 1)]
+        });
+        macro_rules! rngstep(
+            ($j:expr, $shift:expr) => {{
+                let base = $j;
+                let mix = if $shift < 0 {
+                    a >> -$shift as uint
+                } else {
+                    a << $shift as uint
+                };
+
+                let x = self.mem[base  + mr_offset];
+                a = (a ^ mix) + self.mem[base + m2_offset];
+                let y = ind!(x) + a + b;
+                self.mem[base + mr_offset] = y;
+
+                b = ind!(y >> RAND_SIZE_LEN) + x;
+                self.rsl[base + mr_offset] = b;
+            }}
+        );
+
+        let r = [(0, MIDPOINT), (MIDPOINT, 0)];
+        for &(mr_offset, m2_offset) in r.iter() {
+            for i in range_step(0u, MIDPOINT, 4) {
+                rngstep!(i + 0, 13);
+                rngstep!(i + 1, -6);
+                rngstep!(i + 2, 2);
+                rngstep!(i + 3, -16);
+            }
+        }
+
+        self.a = a;
+        self.b = b;
+        self.cnt = RAND_SIZE;
+    }
+}
+
+impl Rng for IsaacRng {
+    #[inline]
+    fn next(&mut self) -> u32 {
+        if self.cnt == 0 {
+            // make some more numbers
+            self.isaac();
+        }
+        self.cnt -= 1;
+        self.rsl[self.cnt]
+    }
+}