1 files changed, 63 insertions, 0 deletions
diff --git a/vendor/image/src/codecs/jpeg/entropy.rs b/vendor/image/src/codecs/jpeg/entropy.rs
new file mode 100644
index 0000000..5bdcef6
--- /dev/null
+++ b/vendor/image/src/codecs/jpeg/entropy.rs
@@ -0,0 +1,63 @@
+/// Given an array containing the number of codes of each code length,
+/// this function generates the huffman codes lengths and their respective
+/// code lengths as specified by the JPEG spec.
+const fn derive_codes_and_sizes(bits: &[u8; 16]) -> ([u8; 256], [u16; 256]) {
+    let mut huffsize = [0u8; 256];
+    let mut huffcode = [0u16; 256];
+
+    let mut k = 0;
+
+    // Annex C.2
+    // Figure C.1
+    // Generate table of individual code lengths
+    let mut i = 0;
+    while i < 16 {
+        let mut j = 0;
+        while j < bits[i as usize] {
+            huffsize[k] = i + 1;
+            k += 1;
+            j += 1;
+        }
+        i += 1;
+    }
+
+    huffsize[k] = 0;
+
+    // Annex C.2
+    // Figure C.2
+    // Generate table of huffman codes
+    k = 0;
+    let mut code = 0u16;
+    let mut size = huffsize[0];
+
+    while huffsize[k] != 0 {
+        huffcode[k] = code;
+        code += 1;
+        k += 1;
+
+        if huffsize[k] == size {
+            continue;
+        }
+
+        // FIXME there is something wrong with this code
+        let diff = huffsize[k].wrapping_sub(size);
+        code = if diff < 16 { code << diff as usize } else { 0 };
+
+        size = size.wrapping_add(diff);
+    }
+
+    (huffsize, huffcode)
+}
+
+pub(crate) const fn build_huff_lut_const(bits: &[u8; 16], huffval: &[u8]) -> [(u8, u16); 256] {
+    let mut lut = [(17u8, 0u16); 256];
+    let (huffsize, huffcode) = derive_codes_and_sizes(bits);
+
+    let mut i = 0;
+    while i < huffval.len() {
+        lut[huffval[i] as usize] = (huffsize[i], huffcode[i]);
+        i += 1;
+    }
+
+    lut
+}