Fix one of many edgecases. I had it right in the comment too.

Author: dequbed

src/engine/avx2/mod.rs

@@ -442,8 +442,8 @@ impl super::Engine for AVX2Encoder {
             // FIXME: Prove this is correct or remove it. Doing an extra fast loop over two bytes
             // is not worth violating safety.
             // 11 => 11, 
-            x if x < 14 => (BLOCKS_PER_FAST_LOOP * 8) + x,
-            x if x >= 14 => x,
+            x if x <= 12 => (BLOCKS_PER_FAST_LOOP * 8) + x,
+            x if x > 12 => x,
             _ => unreachable!("Maths, how does it work?"),
         };
 
@@ -488,6 +488,9 @@ impl super::Engine for AVX2Encoder {
                 // happen is test code that knowingly provides both invalid data and an undersized
                 // buffer assuming linear decoding that breaks off as soon as it hits this invalid
                 // data.
+                if output.len()-output_index < 32 {
+                    println!("IL {} OL {}", input.len(), output.len());
+                }
                 let output_chunk = &mut output[output_index..(output_index + 32)];
 
 
@@ -788,6 +791,7 @@ impl Config for AVX2Config {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::decode::decode_engine;
 
     #[test]
     fn maskload_array_is_sane() {
@@ -801,4 +805,20 @@ mod tests {
         assert_eq!(&MASKLOAD[7..15], &[-1, 0, 0, 0, 0, 0, 0, 0]);
         assert_eq!(&MASKLOAD[8..16], &[ 0, 0, 0, 0, 0, 0, 0, 0]);
     }
+
+    #[test]
+    fn test_every_len() {
+        let engine = AVX2Encoder::from_standard(AVX2Config::new());
+        let mut v = Vec::with_capacity(8192);
+        for i in 1..8192 {
+            v.push('A' as u8);
+            let r = decode_engine(&v, &engine);
+            match i % 4 {
+                1 => assert_eq!(r, Err(DecodeError::InvalidLength)),
+                x => {
+                    assert_eq!(r.unwrap().len(), i*3/4, "Failed on len {}", x);
+                },
+            }
+        }
+    }
 }