Differences

This shows you the differences between two versions of the page.

--- intro_example:pure_struct [2025/05/01 19:58] – rajit
+++ intro_example:pure_struct [2025/05/18 15:07] (current) – rajit
@@ Line 1: / Line 1: @@
 ====== Using pure structures ======
-A [[language:types2:data#pure_structures|pure structure]] is a user-defined data type that contains only ''int''/''bool'' or other pure structures. An example of a pure structure is:
+A [[language:types2:data#pure_structures|pure structure]] is a user-defined data type that contains only ''int''/''bool'' or other pure structures. Pure structures are analogous to C/C++ ''struct''s, and can be used to organize data and
+make CHP more human-readable. An example of a pure structure is:
 <code act>
@@ Line 24: / Line 25: @@
              [] else -> log ("cache miss!"); DO!0
              ]
-     []~cmd -> // write command
+        []~cmd -> // write command
              ce.valid+;
              DI?ce.data;
@@ Line 56: / Line 57: @@
-defproc cache(chan?(int<32>) A; chan?(bool) RD; chan!(int<32>) DI; chan!(int<32>) DO)
+defproc cache(chan?(int<32>) A; chan?(bool) RD; chan?(int<32>) DI; chan!(int<32>) DO)
 {
    cache_entry C[256];
@@ Line 70: / Line 71: @@
              [] else -> log ("cache miss!"); DO!0
              ]
-     []~cmd -> // write command
+       []~cmd -> // write command
              ce.valid+;
              DI?ce.data;
              ce.tag := addr{31..8};
+             C[addr{7..0}] := ce
+      ]
+   ]
+  }
+}
+</code>
+Note that method functions, like other functions in ACT, are pure functions. In other words, they cannot change the fields of the structure. If you need to modify the fields of the structure, special ''macro'' methods are supported. These can contain arbitrary CHP fragments.
+<code act>
+deftype cache_entry (bool valid; int<32> data; int<24> tag)
+{
+    methods {
+        function match (int<32> addr) : bool
+        {
+           chp {
+              self := valid & tag = addr{31..8}
+           }
+         }
+         macro setval (int<32> addr; int<32> dv) {
+            valid+;
+            data := dv;
+            tag := addr{31..8}
+         }
+    }
+}
+defproc cache(chan?(int<32>) A; chan?(bool) RD; chan?(int<32>) DI; chan!(int<32>) DO)
+{
+   cache_entry C[256];
+   int<32> addr, dv;
+   bool cmd;
+   cache_entry ce;
+   chp {
+     *[ A?addr,RD?cmd;
+        [cmd -> // read command
+              ce := C[addr{7..0}];
+             [ ce.match(addr) -> log ("cache hit!"); DO!ce.data
+             [] else -> log ("cache miss!"); DO!0
+             ]
+       []~cmd -> // write command
+             DI?dv;
+             ce.setval (addr, dv);
              C[addr{7..0}] := ce
       ]
@@ Line 88: / Line 133: @@
 <code act>
+int<57> x;
 ...
 chp {
@@ Line 98: / Line 144: @@
 }
 </code>
+The order in which the bits are packed is from left to right in the structure definition, with the left-most field corresponding to the most significant bits of the integer.