From 1c50efbac82c5e159350de46291f8965d88b9410 Mon Sep 17 00:00:00 2001
From: Stephen Chung <schungx@live.com>
Date: Wed, 22 Dec 2021 10:48:19 +0800
Subject: [PATCH] Unroll switch range case if range has only one number.

---
 src/ast/stmt.rs | 38 ++++++++++++++++++++++----------------
 src/parser.rs   | 30 +++++++++++++++++++++++++-----
 2 files changed, 47 insertions(+), 21 deletions(-)

diff --git a/src/ast/stmt.rs b/src/ast/stmt.rs
index c09c3ff5..1754ee56 100644
--- a/src/ast/stmt.rs
+++ b/src/ast/stmt.rs
@@ -144,10 +144,17 @@ impl fmt::Debug for StmtBlock {
     }
 }
 
-impl From<StmtBlock> for Stmt {
-    #[inline(always)]
-    fn from(block: StmtBlock) -> Self {
-        Self::Block(block.0.into_boxed_slice(), block.1)
+impl From<Stmt> for StmtBlock {
+    #[inline]
+    fn from(stmt: Stmt) -> Self {
+        match stmt {
+            Stmt::Block(mut block, pos) => Self(block.iter_mut().map(mem::take).collect(), pos),
+            Stmt::Noop(pos) => Self(StaticVec::new_const(), pos),
+            _ => {
+                let pos = stmt.position();
+                Self(vec![stmt].into(), pos)
+            }
+        }
     }
 }
 
@@ -176,7 +183,13 @@ pub enum Stmt {
     Noop(Position),
     /// `if` expr `{` stmt `}` `else` `{` stmt `}`
     If(Expr, Box<(StmtBlock, StmtBlock)>, Position),
-    /// `switch` expr `if` condition `{` literal or _ `=>` stmt `,` ... `}`
+    /// `switch` expr `{` literal or range or _ `if` condition `=>` stmt `,` ... `}`
+    ///
+    /// ### Data Structure
+    ///
+    /// 0) Hash table for (condition, block)
+    /// 1) Default block
+    /// 2) List of ranges: (start, end, inclusive, condition, statement)
     Switch(
         Expr,
         Box<(
@@ -262,17 +275,10 @@ impl Default for Stmt {
     }
 }
 
-impl From<Stmt> for StmtBlock {
-    #[inline]
-    fn from(stmt: Stmt) -> Self {
-        match stmt {
-            Stmt::Block(mut block, pos) => Self(block.iter_mut().map(mem::take).collect(), pos),
-            Stmt::Noop(pos) => Self(StaticVec::new_const(), pos),
-            _ => {
-                let pos = stmt.position();
-                Self(vec![stmt].into(), pos)
-            }
-        }
+impl From<StmtBlock> for Stmt {
+    #[inline(always)]
+    fn from(block: StmtBlock) -> Self {
+        Self::Block(block.0.into_boxed_slice(), block.1)
     }
 }
 
diff --git a/src/parser.rs b/src/parser.rs
index 2d0601ca..538e990e 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -15,7 +15,7 @@ use crate::tokenizer::{
 };
 use crate::types::dynamic::AccessMode;
 use crate::{
-    calc_fn_hash, calc_qualified_fn_hash, calc_qualified_var_hash, Engine, ExclusiveRange,
+    calc_fn_hash, calc_qualified_fn_hash, calc_qualified_var_hash, Dynamic, Engine, ExclusiveRange,
     Identifier, ImmutableString, InclusiveRange, LexError, ParseError, ParseErrorType, Position,
     Scope, Shared, StaticVec, AST, INT,
 };
@@ -1095,7 +1095,29 @@ fn parse_switch(
 
         def_stmt = match (hash, range) {
             (None, Some(range)) => {
-                ranges.push((range.0, range.1, range.2, condition, stmt.into()));
+                let is_empty = if range.2 {
+                    (range.0..=range.1).is_empty()
+                } else {
+                    (range.0..range.1).is_empty()
+                };
+
+                if !is_empty {
+                    match (range.1.checked_sub(range.0), range.2) {
+                        // Unroll single range
+                        (Some(1), false) | (Some(0), true) => {
+                            let value = Dynamic::from_int(range.0);
+                            let hasher = &mut get_hasher();
+                            value.hash(hasher);
+                            let hash = hasher.finish();
+
+                            if !table.contains_key(&hash) {
+                                table.insert(hash, (condition.clone(), stmt.into()).into());
+                            }
+                        }
+                        // Other range
+                        _ => ranges.push((range.0, range.1, range.2, condition, stmt.into())),
+                    }
+                }
                 None
             }
             (Some(hash), None) => {
@@ -1103,9 +1125,7 @@ fn parse_switch(
                 None
             }
             (None, None) => Some(stmt.into()),
-            (Some(_), Some(_)) => {
-                unreachable!("cannot have both a hash and a range in a `switch` statement")
-            }
+            _ => unreachable!("both hash and range in `switch` statement case"),
         };
 
         match input.peek().expect(NEVER_ENDS) {