nak: Add an implementation of the ACORN random number generator

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30275>

src/nouveau/compiler/acorn/lib.rs

@@ -0,0 +1,81 @@
+// Copyright © 2022 Collabora, Ltd.
+// SPDX-License-Identifier: MIT
+
+// Generated by random.org
+const INIT_DATA: [u16; 64] = [
+    8235, 45378, 61861, 23858, 42241, 27301, 23697, 15333, 52828, 39161, 46572,
+    7478, 11198, 4926, 21736, 23781, 37217, 20323, 32754, 61367, 12882, 35352,
+    29343, 26458, 62858, 44415, 35786, 58466, 45062, 30330, 30350, 35134,
+    28228, 36077, 26793, 27223, 52219, 52544, 3565, 56253, 40962, 40833, 35607,
+    46482, 64735, 31252, 44165, 40273, 46825, 15929, 27160, 1106, 59035, 48146,
+    47365, 19901, 37178, 35614, 29628, 23344, 11328, 60105, 28727, 344,
+];
+
+/// An implementation of the ACORN random number generator
+///
+/// See also http://acorn.wikramaratna.org/concept.html
+///
+/// This isn't cryptographically secure but it's easy and fast and good enough
+/// for generating test data.  More importantly, we own the implementation so it
+/// won't change with random library or compiler upgrades.
+pub struct Acorn {
+    y_n: [u64; Self::K],
+}
+
+impl Acorn {
+    const ORD: usize = 60;
+    const K: usize = 16;
+
+    pub fn new() -> Self {
+        let mut y_0 = [0_u64; Self::K];
+        for m in 0..Self::K {
+            y_0[m] |= u64::from(INIT_DATA[m * 4 + 0]) << 0;
+            y_0[m] |= u64::from(INIT_DATA[m * 4 + 1]) << 16;
+            y_0[m] |= u64::from(INIT_DATA[m * 4 + 2]) << 32;
+            y_0[m] |= u64::from(INIT_DATA[m * 4 + 3]) << 48;
+            y_0[m] &= (1u64 << Self::ORD) - 1;
+        }
+        // For good randomness, the seed should be odd
+        assert!(y_0[0] % 2 == 1);
+        Acorn { y_n: y_0 }
+    }
+
+    fn next_u60(&mut self) -> u64 {
+        // y_n[0] remains uncanged
+        for m in 1..Self::K {
+            // We go in increasing M so y_n[m] is y_(n-1)[m] when we read it but
+            // self.y_n[m - 1] is what it says it is
+            self.y_n[m] = (self.y_n[m] + self.y_n[m - 1]) % (1 << Self::ORD);
+        }
+        self.y_n[Self::K - 1]
+    }
+
+    pub fn get_uint(&mut self, bits: usize) -> u64 {
+        if bits <= Self::ORD {
+            self.next_u60() >> (Self::ORD - bits)
+        } else {
+            let hi = self.next_u60() << (bits - Self::ORD);
+            hi | self.get_uint(bits - Self::ORD)
+        }
+    }
+
+    pub fn get_bool(&mut self) -> bool {
+        self.get_uint(1) != 0
+    }
+
+    pub fn get_u8(&mut self) -> u8 {
+        self.get_uint(8) as u8
+    }
+
+    pub fn get_u16(&mut self) -> u16 {
+        self.get_uint(16) as u16
+    }
+
+    pub fn get_u32(&mut self) -> u32 {
+        self.get_uint(32) as u32
+    }
+
+    pub fn get_u64(&mut self) -> u64 {
+        self.get_uint(64)
+    }
+}

src/nouveau/compiler/meson.build

@@ -66,6 +66,18 @@ libnak_c_files = files(
   'nak_memstream.c',
 )
 
+_libacorn_rs = static_library(
+  'acorn',
+  files('acorn/lib.rs'),
+  gnu_symbol_visibility : 'hidden',
+  rust_abi : 'rust',
+  rust_args : nak_rust_args,
+)
+
+idep_acorn_rs = declare_dependency(
+  link_with : _libacorn_rs,
+)
+
 _libbitview_rs = static_library(
   'bitview',
   files('bitview/lib.rs'),