add: bucket logic, fixed a few bugs

src/lib.rs

@@ -1,6 +1,55 @@
 use nom::{branch::alt, character::complete, IResult};
 use rand::Rng;
 
+#[derive(Debug)]
+pub struct Buckets<const S: usize> {
+    _buckets: [u64; S],
+    _offsets: [i64; S],
+}
+
+impl<const S: usize> Buckets<S> {
+    /// Creates a new bucketer to store the values that can
+    /// be produced by roller in constant-spaced bucket. That
+    /// is, each bucket represents the count of a fixed range,
+    /// and all buckets have the same size range.
+    pub fn new<const R: usize>(roller: &Roller<R>) -> Self {
+        let min = roller.min();
+        let max = roller.max();
+        // Divide the number of buckets we have to work with by the range
+        // Store the step size
+        let step = ((max-min) as usize) / S + 1;
+        let mut _offsets = [0; S];
+        let mut cur = min;
+        for val in _offsets.iter_mut() {
+            *val = cur;
+            cur += step as i64;
+        }
+        Self {
+            _buckets: [0; S],
+            _offsets,
+        }
+    }
+
+    pub fn insert(&mut self, val: i64) {
+        // Binary search to find insertion point
+        let mut pp = self._offsets.partition_point(|p| *p < val);
+        if pp == self._buckets.len() {
+            // This value was beyond the last bucket; go ahead and store if in the
+            // last bucket
+            pp = self.buckets().len()-1;
+        }
+        self._buckets[pp] += 1;
+    }
+
+    pub fn buckets(&self) -> &[u64] {
+        &self._buckets[..]
+    }
+
+    pub fn labels(&self) -> &[i64] {
+        &self._offsets[..]
+    }
+}
+
 pub struct Roller<const S: usize> {
     exprs: [Option<Cmd>; S],
 }
@@ -31,7 +80,7 @@ impl<const S: usize> Roller<S> {
         }
         Ok(Roller{exprs})
     }
-    pub fn roll<R: Rng>(&self, rng: &mut R) -> u64 {
+    pub fn roll<R: Rng>(&self, rng: &mut R) -> i64 {
         let mut sum = 0;
         for expr in &self.exprs {
             if expr.is_none() {
@@ -39,8 +88,38 @@ impl<const S: usize> Roller<S> {
             }
             let cmd = expr.as_ref().unwrap();
             match cmd.oper {
-                Oper::Add => sum += cmd.term.val(rng),
-                Oper::Sub => sum -= cmd.term.val(rng),
+                Oper::Add => sum += cmd.term.val(rng) as i64,
+                Oper::Sub => sum -= cmd.term.val(rng) as i64,
+            };
+        }
+        sum
+    }
+
+    pub fn min(&self) -> i64 {
+        let mut sum = 0;
+        for expr in &self.exprs {
+            if expr.is_none() {
+                break;
+            }
+            let cmd = expr.as_ref().unwrap();
+            match cmd.oper {
+                Oper::Add => sum += cmd.term.min() as i64,
+                Oper::Sub => sum -= cmd.term.min() as i64,
+            };
+        }
+        sum
+    }
+
+    pub fn max(&self) -> i64 {
+        let mut sum = 0;
+        for expr in &self.exprs {
+            if expr.is_none() {
+                break;
+            }
+            let cmd = expr.as_ref().unwrap();
+            match cmd.oper {
+                Oper::Add => sum += cmd.term.max() as i64,
+                Oper::Sub => sum -= cmd.term.max() as i64,
             };
         }
         sum
@@ -64,6 +143,20 @@ impl Term {
             Term::Roll(r) => r.val(rng),
         }
     }
+
+    fn min(&self) -> u64 {
+        match self {
+            Term::Const(c) => *c,
+            Term::Roll(r) => r.min(),
+        }
+    }
+    
+    fn max(&self) -> u64 {
+        match self {
+            Term::Const(c) => *c,
+            Term::Roll(r) => r.max(),
+        }
+    }
 }
 
 #[derive(Clone, Copy)]
@@ -85,6 +178,16 @@ impl Roll {
         }
         total
     }
+
+    fn min(&self) -> u64 {
+        // Roll a 1 on each dice
+        self.reps
+    }
+
+    fn max(&self) -> u64 {
+        // Roll max on each dice
+        self.reps * self.dice
+    }
 }
 
 
@@ -127,13 +230,13 @@ mod tests {
     fn roll_many_d6s() {
         let mut rng = StdRng::seed_from_u64(1337);
         let roller = Roller::<1024>::parse("1d6").unwrap();
-        let mut results = [0u64; 6];
+        let mut buckets = Buckets::<6>::new(&roller);
         for _ in 0..1000 {
-            results[(roller.roll(&mut rng)-1) as usize] += 1;
+            buckets.insert(roller.roll(&mut rng));
         }
         // We should have some in each bucket
-        for x in results {
-            assert!(x > 50);
+        for x in buckets.buckets() {
+            assert!(*x > 50);
         }
     }
 
@@ -141,45 +244,72 @@ mod tests {
     fn roll_many_d6s_plus_2() {
         let mut rng = StdRng::seed_from_u64(1337);
         let roller = Roller::<1024>::parse("1d6+2").unwrap();
-        let mut results = [0u64; 6+2];
+        let mut buckets = Buckets::<6>::new(&roller);
         for _ in 0..1000 {
-            results[(roller.roll(&mut rng)-1) as usize] += 1;
+            buckets.insert(roller.roll(&mut rng));
         }
-        // Can't get a 1 or 2, but should have many others
-        assert!(results[0] == 0);
-        assert!(results[1] == 0);
-        for x in &results[2..] {
+        // We should have some in each bucket
+        for x in buckets.buckets() {
             assert!(*x > 50);
         }
+
+        // The first bucket should be 3 (1 on a d6, +2)
+        assert_eq!(buckets.labels()[0], 3);
+        // Last bucket should be 8
+        assert_eq!(buckets.labels()[5], 8);
     }
 
     #[test]
     fn roll_many_d6s_plus_1d6() {
         let mut rng = StdRng::seed_from_u64(1337);
         let roller = Roller::<1024>::parse("1d6+1d6").unwrap();
-        let mut results = [0u64; 6+6];
+        let mut buckets = Buckets::<6>::new(&roller);
         for _ in 0..1000 {
-            results[(roller.roll(&mut rng)-1) as usize] += 1;
+            buckets.insert(roller.roll(&mut rng));
         }
-        // Its impossible to roll 1
-        assert!(results[0] == 0);
-        for x in &results[1..] {
+        // We should have some in each bucket
+        for x in buckets.buckets() {
             assert!(*x > 1);
         }
+
+        // The first bucket should be 2
+        assert_eq!(buckets.labels()[0], 2);
+        // Last bucket should be 12
+        assert_eq!(buckets.labels()[5], 12);
     }
 
     #[test]
     fn roll_many_d6s_plus_1d6_minus_one() {
         let mut rng = StdRng::seed_from_u64(1337);
         let roller = Roller::<1024>::parse("1d6+1d6-1").unwrap();
-        let mut results = [0u64; 6+6];
+        let mut buckets = Buckets::<6>::new(&roller);
         for _ in 0..1000 {
-            results[(roller.roll(&mut rng)-1) as usize] += 1;
+            buckets.insert(roller.roll(&mut rng));
         }
-        // Its impossible to roll 12
-        assert!(results[11] == 0);
-        for x in &results[..11] {
+        // We should have some in each bucket
+        for x in buckets.buckets() {
             assert!(*x > 1);
         }
+
+        // The first bucket should be 1
+        assert_eq!(buckets.labels()[0], 1);
+        // Last bucket should be 11
+        assert_eq!(buckets.labels()[5], 11);
+    }
+
+    #[test]
+    fn negative_result() {
+        let mut rng = StdRng::seed_from_u64(1337);
+        let roller = Roller::<1024>::parse("1d6-5").unwrap();
+        for _ in 0..1000 {
+            roller.roll(&mut rng);
+        }
+    }
+
+    #[test]
+    fn min_max() {
+        let roller = Roller::<1024>::parse("2d6+1d8+1").unwrap();
+        assert_eq!(roller.min(), 4);
+        assert_eq!(roller.max(), 21);
     }
 }