TMP

server/src/main.rs

@@ -43,6 +43,7 @@ pub enum Format {
     Gray8,
     Gray8Simd,
     Gray16be,
+    Pal4,
 }
 
 impl Format {
@@ -98,6 +99,16 @@ impl Format {
                     tgt.write_all(&buf[0..OUT])?;
                 }
             }
+
+            Self::Pal4 => {
+                const OUT: usize = reduce::pal4::out_size(IN_SIZE);
+                let mut buf = [0u8; IN_SIZE];
+                loop {
+                    src.read_exact(&mut buf)?;
+                    reduce::pal4::run(&mut buf);
+                    tgt.write_all(&buf[0..OUT])?;
+                }
+            }
         }
     }
 }

server/src/reduce/mod.rs

@@ -2,3 +2,4 @@ pub mod gray8;
 pub mod gray8_simd;
 pub mod mono;
 pub mod mono_simd;
+pub mod pal4;

server/src/reduce/pal4.rs

@@ -0,0 +1,37 @@
+use std::convert::TryInto;
+
+const GROUP_BY: usize = 8;
+pub const fn out_size(in_size: usize) -> usize {
+    in_size / 8
+}
+
+pub fn run(buf: &mut [u8]) {
+    let n_raw = buf.len();
+    let mut in_cursor = 0;
+    let mut out_cursor = 0;
+
+    while in_cursor + GROUP_BY <= n_raw {
+        let a: &[u8; 8] = buf[in_cursor..in_cursor + 8].try_into().unwrap();
+
+        let pix = [a[0], a[2], a[4], a[6]];
+
+        let mut out = 0u8;
+
+        for i in 0..pix.len() {
+            let p = pix[i] & 0b1110;
+            if p >= 0x0E {
+                out |= 0b11 >> (2 * i);
+            } else if p >= 0x04 {
+                out |= 0b10 >> (2 * i);
+            } else if p >= 0x01 {
+                out |= 0b01 >> (2 * i);
+            } else {
+                out |= 0b00 >> (2 * i);
+            }
+        }
+
+        buf[out_cursor] = out;
+        out_cursor += 1;
+        in_cursor += GROUP_BY;
+    }
+}