#66: Added description of file format

README.md

@@ -11,15 +11,41 @@ $ build/chai <app.chai>
 ### Chai bytecode currently is just a Sequence of instructions.
 For instance, there is disassembler of simple app.chai
 ```
-Ldia 6
-Star r2
-Ldia 8
-Star r3
-Ldra r3
-Mul r2
-Printc acc
-Mov o r0
-Ret
+fn main 8 0:
+  Ldia 6
+  Star r2
+  Ldia 8
+  Star r3
+  Ldra r3
+  Mul r2
+  Printc acc
+  Mov 0 r0
+  Ret
 ```
-Where Ret returns exit code `r0`.
+Where Ret returns exit code `r0`. "main" is name of the starting function, `8` is number of registers in it, `0` is number of arguments passing into the function. 
 This script compiled to chai-bytecode should print "0", because '0' == 48.
+## Chai file format
+Our file format is similar to jvm ClassFile Structure. Its content is the following:
+- Constants count (`imm`)
+- Constant[]
+- func_info count (`imm`)
+- func_info[]
+
+Where `imm` is 2 bytes.
+
+`Constant` has a 1 byte tag that specifies its type(ConstI64, or ConstFuncNameAndType and so on) and the payload then.
+
+`func_info` structure:
+```
+func_info {
+  imm accessFlagsCount
+  imm ConstFuncNameAndType
+  imm attsCount                // Count of attributes. Now only Code attribute exists
+  imm attNameIndex             // Id of attribute, Now can be arbitrary
+  imm attLen                   // Size of the Code atribute in bytes 
+  u1 maxRegisters              // Number of registers used in function
+  u1 nargs                     // Number of arguments to pass
+  u4 codeLen                   // Size of code(instructions only) in bytes
+  u1[] code                    // Instructions, byte array.
+}         
+```