Shrink numeric types

src/compression.rs

@@ -5,14 +5,14 @@ use crate::{constants::{MAGIC, TILE_SZ, TILE_SZ2}, protocol::{self, ProtocolWrit
 
 struct PixelTile {
     // i32: representation that supports Walsh-Hadamard
-    pixels: [i32; TILE_SZ2]
+    pixels: [i16; TILE_SZ2]
 }
 struct CoefTile {
-    coefs: [i32; TILE_SZ2]
+    coefs: [i16; TILE_SZ2]
 }
 
 struct QuantTile {
-    quants: [i32; TILE_SZ2]
+    quants: [i16; TILE_SZ2]
 }
 
 
@@ -75,7 +75,7 @@ impl PixelTile {
                 let src_y = y0 + y;
                 pixels[y * TILE_SZ + x] = 
                     if src_x < width && src_y < height { 
-                        layer[src_y * width + src_x] as i32
+                        layer[src_y * width + src_x] as i16
                     } else {
                         0
                     };
@@ -112,13 +112,13 @@ impl QuantTile {
     }
 
     fn write_zero<W: Write>(&self, writer: &mut ProtocolWriter<W>) -> ProtocolWriterResult<()> {
-        writer.write_i32_packed(self.quants[0])?;
+        writer.write_i16_wide(self.quants[0])?;
         Ok(())
     }
 
     fn write_rest<W: Write>(&self, writer: &mut ProtocolWriter<W>) -> ProtocolWriterResult<()> {
         for i in 1..self.quants.len() {
-            writer.write_i32_packed(self.quants[i])?;
+            writer.write_i16_packed(self.quants[i])?;
         }
         Ok(())
     }

src/decompression.rs

@@ -4,17 +4,17 @@ use crate::{constants::{MAGIC, TILE_SZ, TILE_SZ2}, protocol::{ProtocolReader, Pr
 
 struct PixelTile {
     // i32: representation that supports Walsh-Hadamard
-    pixels: [i32; TILE_SZ2]
+    pixels: [i16; TILE_SZ2]
 }
 
 #[derive(Clone)]
 struct CoefTile {
-    coefs: [i32; TILE_SZ2]
+    coefs: [i16; TILE_SZ2]
 }
 
 #[derive(Clone)]
 struct QuantTile {
-    quants: [i32; TILE_SZ2]
+    quants: [i16; TILE_SZ2]
 }
 
 pub fn decompress<R: Read>(
@@ -93,11 +93,11 @@ impl PixelTile {
         }
     }
     
-    fn clip(&self, x: i32) -> u8 {
-        if x > u8::MAX as i32 {
+    fn clip(&self, x: i16) -> u8 {
+        if x > u8::MAX as i16 {
             return u8::MAX
         }
-        if x < u8::MIN as i32 {
+        if x < u8::MIN as i16 {
             return u8::MIN;
         }
         return x as u8;
@@ -116,13 +116,13 @@ impl QuantTile {
     }
 
     fn load_zero<R: Read>(&mut self, reader: &mut ProtocolReader<R>) -> ProtocolReaderResult<()> {
-        self.quants[0] = reader.read_i32_packed()?;
+        self.quants[0] = reader.read_i16_wide()?;
         Ok(())
     }
 
     fn load_rest<R: Read>(&mut self, reader: &mut ProtocolReader<R>) -> ProtocolReaderResult<()> {
         for i in 1..self.quants.len() {
-            self.quants[i] = reader.read_i32_packed()?;
+            self.quants[i] = reader.read_i16_packed()?;
         }
         Ok(())
     }

src/protocol.rs

@@ -61,21 +61,19 @@ impl<W: Write> ProtocolWriter<W> {
         self.writer.write_all(&value.to_le_bytes())?;
         Ok(())
     }
-    pub fn write_i32_packed(&mut self, value: i32) -> ProtocolWriterResult<()> {
+    pub fn write_i16_wide(&mut self, value: i16) -> ProtocolWriterResult<()> {
+        self.writer.write_all(&value.to_le_bytes())?;
+        Ok(())
+    }
+    pub fn write_i16_packed(&mut self, value: i16) -> ProtocolWriterResult<()> {
         // We reserve i8::MAX and i16::MAX as signal values that `value` is too big
         // for each respective type
-        if (i8::MIN as i32..i8::MAX as i32).contains(&value) {
+        if (i8::MIN as i16..i8::MAX as i16).contains(&value) {
             self.writer.write_all(&(value as i8).to_le_bytes())?;
             return Ok(())
         } 
         self.writer.write_all(&(i8::MAX).to_le_bytes())?;
-
-        if (i16::MIN as i32..i16::MAX as i32).contains(&value) {
-            self.writer.write_all(&(value as i16).to_le_bytes())?;
-            return Ok(())
-        } 
-        self.writer.write_all(&(i16::MAX).to_le_bytes())?;
-        self.writer.write_all(&value.to_le_bytes())?;
+        self.writer.write_all(&(value as i16).to_le_bytes())?;
         Ok(())
     }
 }
@@ -105,21 +103,23 @@ impl<R: Read> ProtocolReader<R> {
         Ok(u32::from_le_bytes(u32_buf))
     }
 
-    pub fn read_i32_packed(&mut self) -> ProtocolReaderResult<i32> {
+    pub fn read_i16_wide(&mut self) -> ProtocolReaderResult<i16> {
+        let mut i16_buf = [0; 2];
+        self.read_exact(&mut i16_buf)?;
+
+        Ok(i16::from_le_bytes(i16_buf))
+    }
+
+    pub fn read_i16_packed(&mut self) -> ProtocolReaderResult<i16> {
         let mut i8_buf = [0; 1];
         self.read_exact(&mut i8_buf)?;
         let i8_value = i8::from_le_bytes(i8_buf);
-        if i8_value != i8::MAX { return Ok(i8_value as i32) }
+        if i8_value != i8::MAX { return Ok(i8_value as i16) }
 
         let mut i16_buf = [0; 2];
         self.read_exact(&mut i16_buf)?;
         let i16_value = i16::from_le_bytes(i16_buf);
-        if i16_value != i16::MAX { return Ok(i16_value as i32) }
-
-        let mut i32_buf = [0; 4];
-        self.read_exact(&mut i32_buf)?;
-        let i32_value = i32::from_le_bytes(i32_buf);
-        Ok(i32_value)
+        Ok(i16_value as i16) 
     }
 
     // wrap UnexpectedEof, since that's an error for other Io clients,

src/quantization.rs

@@ -12,9 +12,9 @@ const ZIGZAG: [u8; TILE_SZ2] = [
 ];
 
 pub fn to_quantized(
-    coefs: [i32; TILE_SZ2]
-) -> [i32; TILE_SZ2] {
-    let mut quant: [i32; TILE_SZ2] = [0; TILE_SZ2];
+    coefs: [i16; TILE_SZ2]
+) -> [i16; TILE_SZ2] {
+    let mut quant: [i16; TILE_SZ2] = [0; TILE_SZ2];
 
     for cf_ix in 0..TILE_SZ2 {
         let div = divisor(cf_ix);
@@ -35,21 +35,21 @@ pub fn to_quantized(
 }
 
 pub fn from_quantized(
-    quant: [i32; TILE_SZ2]
-) -> [i32; TILE_SZ2] {
-    let mut coefs: [i32; TILE_SZ2] = [0; TILE_SZ2];
+    quant: [i16; TILE_SZ2]
+) -> [i16; TILE_SZ2] {
+    let mut coefs: [i16; TILE_SZ2] = [0; TILE_SZ2];
     for cf_ix in 0..TILE_SZ2 {
         let div = divisor(cf_ix);
-        coefs[cf_ix] = quant[ZIGZAG[cf_ix] as usize] * div;
+        coefs[cf_ix] = quant[ZIGZAG[cf_ix] as usize].wrapping_mul(div);
     }
     coefs
 }
 
-pub fn divisor(cf_ix: usize) -> i32 {
+pub fn divisor(cf_ix: usize) -> i16 {
     if cf_ix == 0 { return 1; }
     let x = cf_ix % 8;
     let y = cf_ix / 8;
-    let div = 32 + (x as i32 + y as i32) * 12;
+    let div = 32 + (x as i16 + y as i16) * 12;
     if div==32 && cf_ix != 0 {
         dbg!(cf_ix, x, y, div);
     }

src/transform.rs

@@ -3,15 +3,15 @@ use crate::constants::TILE_SZ;
 // This is the Walsh-Hadamard transform, specialized to 8px
 // Ported from: 
 // - https://colab.research.google.com/drive/1WjtKwUcqxWafAumFO9ET74RsckZSsw6n#scrollTo=e3r9-RBpcgwH
-pub fn encode(data: &mut [i32], zero: usize, stride: usize) {
+pub fn encode(data: &mut [i16], zero: usize, stride: usize) {
     transform(data, zero, stride, 0, 0, 1)
 }
 
-pub fn decode(data: &mut [i32], zero: usize, stride: usize) {
+pub fn decode(data: &mut [i16], zero: usize, stride: usize) {
     transform(data, zero, stride, 0, 0, 8)
 }
 
-fn transform(data: &mut [i32], zero: usize, stride: usize, offset_in: i32, offset_out: i32, divisor: i32) {
+fn transform(data: &mut [i16], zero: usize, stride: usize, offset_in: i16, offset_out: i16, divisor: i16) {
     let ix = |t| zero + t * stride;
 
     let mut row = [0; TILE_SZ];
@@ -47,13 +47,16 @@ mod tests {
     use crate::{constants::TILE_SZ, transform::{decode, encode}};
 
     #[derive(Clone, Debug)]
-    struct Encodable { args: [i32; TILE_SZ] }
+    struct Encodable { args: [i16; TILE_SZ] }
 
     impl Arbitrary for Encodable {
         fn arbitrary(g: &mut quickcheck::Gen) -> Self {
             let mut args = [0; TILE_SZ];
             for i in 0..TILE_SZ {
-                args[i] = i16::arbitrary(g) as i32;
+                args[i] = (
+                    i8::arbitrary(g).signum() as i32 * 
+                    (i32::arbitrary(g) % 255 * 16)
+                ) as i16;
             }
             return Encodable { args };
         }