docs(examples): introduce select example

docs/SUMMARY.md

@@ -6,6 +6,7 @@
   - [Compiling Zink Project](./tutorial/compile-zink-project.md)
 - [Examples](./examples/README.md)
   - [AddTwo](./examples/add-two.md)
+  - [Select](./examples/select.md)
   - [Fibonacci](./examples/fibonacci.md)
 - [Command Line Tool](./cli/README.md)
   - [elko](./cli/elko.md)

docs/examples/README.md

@@ -2,10 +2,12 @@
 
 This chapter provides various zink examples in rust:
 
-| name                     | knowledges                                 | description              |
-| ------------------------ | ------------------------------------------ | ------------------------ |
-| [`add-two`][add-two]     | `params`                                   | basic program in zink    |
-| [`fibonacci`][fibonacci] | `params`, `calls`, `recursion`, `if-block` | recursion implementation |
+| name                     | knowledges                                 | description                                       |
+|--------------------------|--------------------------------------------|---------------------------------------------------|
+| [`add-two`][add-two]     | `params`                                   | basic program in zink                             |
+| [`if-else`][if-else]     | `params`, `code-section`         | program with extra instruction `select` from WASM |
+| [`fibonacci`][fibonacci] | `params`, `calls`, `recursion`, `if-block` | recursion implementation                          |
 
 [add-two]: /examples/add-two.md
+[if-else]: /examples/if-else.md
 [fibonacci]: /examples/fibonacci.md

docs/examples/add-two.md

@@ -14,3 +14,24 @@ pub extern "C" fn addition(x: u64, y: u64) -> u64 {
     x + y
 }
 ```
+
+A basic addition program in zink
+
+```wasm
+(module
+    (func (param i32) (param i32) (result i32)
+    (local.get 0)
+    (local.get 1)
+    (i32.add)
+    )
+)
+```
+
+Requires: 
+- Get params from locals
+- Process basic operand
+- Return data from the result type
+
+```text
+6000356020350160005260206000f3
+```

docs/examples/fibonacci.md

@@ -24,3 +24,46 @@ pub extern "C" fn recursion(n: usize) -> usize {
     }
 }
 ```
+
+A recursion example, complex in bytecode
+
+```wasm
+(module
+  (type (;0;) (func (param i32) (result i32)))
+  (func (;0;) (type 0) (param i32) (result i32)
+    local.get 0
+    call 1)
+  (func (;1;) (type 0) (param i32) (result i32)
+    (local i32)
+    local.get 0
+    i32.const 2
+    i32.ge_u
+    if  ;; label = @1
+      loop  ;; label = @2
+        local.get 0    ;; 1
+        i32.const 1    ;; 2
+        i32.sub        ;; 1
+        call 1         ;; 1
+        local.get 1    ;; 2
+        i32.add        ;; 1
+        local.set 1    ;; 0
+        local.get 0    ;; 1
+        i32.const 2    ;; 2
+        i32.sub        ;; 1
+        local.tee 0    ;; 1
+        i32.const 1    ;; 2
+        i32.gt_u       ;; 1
+        br_if 0 (;@2;) ;; 2 -> 0
+      end
+    end
+    local.get 0
+    local.get 1
+    i32.add))
+```
+
+A more complex implementation of locals ( params + local variables) is introduced in this example,
+control flow `br_if` and `loop` are compiled as well.
+
+```
+600035586010565b60005260206000f35b906000816002600190031015603d575b8160019003586010565b8101905081600290038092506001106020575b8181019150509060040156
+```

docs/examples/if-else.md

@@ -0,0 +1 @@
+# AddTwo

docs/examples/select.md

@@ -0,0 +1,44 @@
+# Select
+
+
+```rust
+//! if-else example.
+#![no_std]
+
+// for the panic handler.
+#[cfg(not(test))]
+extern crate zink;
+
+/// Simple if-else condition
+#[no_mangle]
+pub extern "C" fn if_else(x: u64, y: u64) -> u64 {
+    if x > y {
+        x
+    } else {
+        y
+    }
+}
+
+```
+
+Code block selecting value with if-else will be compiled to instruction `select` in WASM
+
+```wasm
+(module
+  (type (;0;) (func (param i64 i64) (result i64)))
+  (func $if_else (type 0) (param i64 i64) (result i64)
+    local.get 0
+    local.get 1
+    local.get 0
+    local.get 1
+    i64.gt_u
+    select))
+```
+
+Since EVM bytecode doesn't have similar instruction, we have to implement it ourselves, the solution
+is introduce a `select` function in the extra code section provided by zink compiler, jump to there
+and jump back just like calling a real function.
+
+```
+60003560203560003560203510589190601c575b60005260206000f35b5060060156
+```