Fixed a bunch of problems that came up when running debug build.

The worst offender was an obvious and nasty bug in the bitstack
implementation.  Hooray for debug asserts!

src/bitstack.rs

@@ -18,8 +18,10 @@ impl BitStack128 {
 
     /// Push a bit onto the top of the stack.
     pub fn push(&mut self, value: bool) {
-        debug_assert!((self.data.1 >> (size_of::<u64>() - 1)) == 0); // Verify no stack overflow
-        self.data.1 = (self.data.1 << 1) | (self.data.0 >> (size_of::<u64>() - 1));
+        // Verify no stack overflow
+        debug_assert!((self.data.1 >> ((size_of::<u64>() * 8) - 1)) == 0);
+
+        self.data.1 = (self.data.1 << 1) | (self.data.0 >> ((size_of::<u64>() * 8) - 1));
         self.data.0 <<= 1;
         self.data.0 |= value as u64;
     }
@@ -35,12 +37,12 @@ impl BitStack128 {
     /// bits are non-zero this will produce incorrect results.
     pub fn push_n(&mut self, value: u8, count: u8) {
         // Verify no bitstack overflow
-        debug_assert!((self.data.1 >> (size_of::<u64>() - count as usize)) == 0);
+        debug_assert!((self.data.1 >> ((size_of::<u64>() * 8) - count as usize)) == 0);
         // Verify no bits outside of the n-bit range
         debug_assert!(value & (!((1 << count) - 1)) == 0);
 
         self.data.1 = (self.data.1 << count as usize) |
-                      (self.data.0 >> (size_of::<u64>() - count as usize));
+                      (self.data.0 >> ((size_of::<u64>() * 8) - count as usize));
         self.data.0 <<= count as u64;
         self.data.0 |= value as u64;
     }
@@ -48,7 +50,7 @@ impl BitStack128 {
     /// Pop the top bit off the stack.
     pub fn pop(&mut self) -> bool {
         let b = (self.data.0 & 1) != 0;
-        self.data.0 = (self.data.0 >> 1) | (self.data.1 << (size_of::<u64>() - 1));
+        self.data.0 = (self.data.0 >> 1) | (self.data.1 << ((size_of::<u64>() * 8) - 1));
         self.data.1 >>= 1;
         return b;
     }
@@ -57,10 +59,10 @@ impl BitStack128 {
     /// an integer, with the top bit in the least significant digit,
     /// and the rest following in order from there.
     pub fn pop_n(&mut self, n: usize) -> u64 {
-        debug_assert!(n < size_of::<BitStack128>()); // Can't pop more than we have
-        debug_assert!(n < size_of::<u64>()); // Can't pop more than the return type can hold
+        debug_assert!(n < (size_of::<BitStack128>() * 8)); // Can't pop more than we have
+        debug_assert!(n < (size_of::<u64>() * 8)); // Can't pop more than the return type can hold
         let b = self.data.0 & ((1 << n) - 1);
-        self.data.0 = (self.data.0 >> n) | (self.data.1 << (size_of::<u64>() - n));
+        self.data.0 = (self.data.0 >> n) | (self.data.1 << ((size_of::<u64>() * 8) - n));
         self.data.1 >>= n;
         return b;
     }
@@ -74,8 +76,11 @@ impl BitStack128 {
     /// are returned as an integer, with the top bit in the least
     /// significant digit, and the rest following in order from there.
     pub fn peek_n(&self, n: usize) -> u64 {
-        debug_assert!(n < size_of::<BitStack128>()); // Can't return more than we have
-        debug_assert!(n < size_of::<u64>()); // Can't return more than the return type can hold
+        // Can't return more than we have
+        debug_assert!(n < (size_of::<BitStack128>() * 8));
+        // Can't return more than the return type can hold
+        debug_assert!(n < (size_of::<u64>() * 8));
+
         self.data.0 & ((1 << n) - 1)
     }
 }

src/renderer.rs

@@ -202,8 +202,16 @@ impl<'a> Renderer<'a> {
 
                 let x = bx as usize * bucket_w;
                 let y = by as usize * bucket_h;
-                let w = min(bucket_w, img_width - x);
-                let h = min(bucket_h, img_height - y);
+                let w = if img_width >= x {
+                    min(bucket_w, img_width - x)
+                } else {
+                    bucket_w
+                };
+                let h = if img_height >= y {
+                    min(bucket_h, img_height - y)
+                } else {
+                    bucket_h
+                };
                 if x < img_width && y < img_height && w > 0 && h > 0 {
                     job_queue.push(BucketJob {
                         x: x as u32,

src/shading/surface_closure.rs

@@ -342,7 +342,7 @@ pub struct GTRClosure {
     col: XYZ,
     roughness: f32,
     tail_shape: f32,
-    fresnel: f32,
+    fresnel: f32, // [0.0, 1.0] determines how much fresnel reflection comes into play
     normalization_factor: f32,
 }
 
@@ -372,6 +372,8 @@ impl GTRClosure {
 
     // Makes sure values are in a valid range
     fn validate(&mut self) {
+        debug_assert!(self.fresnel >= 0.0 && self.fresnel <= 1.0);
+
         // Clamp values to valid ranges
         self.roughness = clamp(self.roughness, 0.0, 0.9999);
         self.tail_shape = (0.0001f32).max(self.tail_shape);

src/surface/triangle_mesh.rs

@@ -115,7 +115,7 @@ impl<'a> Surface for TriangleMesh<'a> {
                                                                                              0.8),
                                                                                     0.1,
                                                                                     2.0,
-                                                                                    1.2)),
+                                                                                    1.0)),
                             };
                             r.max_t = t;
                         }