modules/zstd: Add FSE probability frequency decoder

Internal-tag: [#55149]
Signed-off-by: Robert Winkler <rwinkler@antmicro.com>

xls/modules/zstd/BUILD

@@ -677,3 +677,19 @@ xls_dslx_test(
     },
     library = ":shift_buffer_dslx",
 )
+
+xls_dslx_library(
+    name = "fse_proba_freq_dec_dslx",
+    srcs = ["fse_proba_freq_dec.x"],
+    deps = [
+        ":shift_buffer_dslx",
+        ":common_dslx",
+        "//xls/examples:ram_dslx",
+    ],
+)
+
+xls_dslx_test(
+    name = "fse_proba_freq_dec_dslx_test",
+    dslx_test_args = {"compare": "none"},
+    library = ":fse_proba_freq_dec_dslx",
+)

xls/modules/zstd/common.x

@@ -16,9 +16,12 @@ pub const DATA_WIDTH = u32:64;
 pub const MAX_ID = u32::MAX;
 pub const SYMBOL_WIDTH = u32:8;
 pub const BLOCK_SIZE_WIDTH = u32:21;
+pub const BLOCK_PACKET_WIDTH = u32:32;
+pub const FSE_MAX_SYMBOLS = u32:256;
+pub const FSE_MAX_ACCURACY_LOG = u32:9;
 
 pub type BlockData = bits[DATA_WIDTH];
-pub type BlockPacketLength = u32;
+pub type BlockPacketLength = bits[BLOCK_PACKET_WIDTH];
 pub type BlockSize = bits[BLOCK_SIZE_WIDTH];
 pub type CopyOrMatchContent = BlockData;
 pub type CopyOrMatchLength = u64;
@@ -54,3 +57,30 @@ pub struct SequenceExecutorPacket {
     content: CopyOrMatchContent, // Literal data or match offset
     last: bool, // Last packet in frame
 }
+
+pub enum CompressionMode : u2 {
+    PredefinedMode    = 0,
+    RLEMode           = 1,
+    FSECompressedMode = 2,
+    RepeatMode        = 3,
+}
+
+pub struct SequenceConf {
+    sequence_count: u17,
+    literals_mode: CompressionMode,
+    offset_mode: CompressionMode,
+    match_mode: CompressionMode,
+}
+
+pub struct SequencePathCtrl {
+    literals_count: u20,
+    last_block: bool,
+    id: u32,
+    sequence_conf: SequenceConf,
+}
+
+pub struct SequenceData {
+    bytes: bits[64],
+    length: u32,
+    last: bool,
+}