JACOBIN-590 Experimenting with some of the ideas presented in JACOBIN…

…-590

src/config/buildno.go

@@ -8,4 +8,4 @@
 
 package config
 
-var BuildNo = 3067
+var BuildNo = 3068

src/config/version.go

@@ -10,7 +10,7 @@ import "strconv"
 
 // v 0.6.0 begun 8/31/24 at 3,012 GitHub commits
 
-var JacobinVersion = "0.6.012"
+var JacobinVersion = "0.6.013"
 
 // GetJacobinVersion returns a manually updated version number and an
 // automatically updated build #. The latter being updated by bumpbuildno.go

src/jvm/interpreter.go

@@ -0,0 +1,83 @@
+/*
+ * Jacobin VM - A Java virtual machine
+ * Copyright (c) 2024 by  the Jacobin Authors. All rights reserved.
+ * Licensed under Mozilla Public License 2.0 (MPL 2.0)  Consult jacobin.org.
+ */
+
+/* ================================================
+   THIS IS AN EXPERIMENTAL ALTERNATIVE TO run.go
+   The chages it makes:
+   * Uses an array of functions rather than a switch for each bytecode
+   * Does only one push and pull for 64-bit values (longs and doubles)
+*/
+
+package jvm
+
+import (
+	"jacobin/frames"
+	"jacobin/object"
+)
+
+// set up a DispatchTable with 256 slots that correspond to the bytecodes
+// each slot being a pointer to a function that accepts a pointer to the
+// current frame and an int parameter. It returns an int that indicates
+// how much to increase that frame's PC (program counter) by.
+type BytecodeFunc func(*frames.Frame, int64) int
+
+var DispatchTable = [256]BytecodeFunc{
+	doNop,        // NOP         0x00
+	doAconstNull, // ACONST_NULL 0x01
+	doIconstM1,   // ICONST_M1   0x02
+	doIconst0,    // ICONST_0    0x03
+	doIconst1,    // ICONST_1    0x04
+	doIconst2,    // ICONST_2    0x05
+	doIconst3,    // ICONST_3    0x06
+	doIconst4,    // ICONST_4    0x07
+	doIconst5,    // ICONST_5    0x08
+	doLconst0,    // LCONST_0    0x09
+	doLconst1,    // LCONST_1    0x0A
+	doFconst0,    // FCONST_0    0x0B
+	doFconst1,    // FCONST_1    0x0C
+	doFconst2,    // FCONST_2    0x0D
+	doDconst0,    // DCONST_0    0x0E
+	doDconst1,    // DCONST_1    0x0F
+}
+
+// the functions, listed here in numerical order of the bytecode
+func doNop(_ *frames.Frame, _ int64) int { return 1 }
+func doAconstNull(f *frames.Frame, _ int64) int {
+	push(f, object.Null)
+	return 1
+}
+
+func doIconstM1(f *frames.Frame, _ int64) int { return pushInt(f, int64(-1)) }
+func doIconst0(f *frames.Frame, _ int64) int  { return pushInt(f, int64(0)) }
+func doIconst1(f *frames.Frame, _ int64) int  { return pushInt(f, int64(1)) }
+func doIconst2(f *frames.Frame, _ int64) int  { return pushInt(f, int64(2)) }
+func doIconst3(f *frames.Frame, _ int64) int  { return pushInt(f, int64(3)) }
+func doIconst4(f *frames.Frame, _ int64) int  { return pushInt(f, int64(4)) }
+func doIconst5(f *frames.Frame, _ int64) int  { return pushInt(f, int64(5)) }
+func doLconst0(f *frames.Frame, _ int64) int  { return pushInt(f, int64(0)) }
+func doLconst1(f *frames.Frame, _ int64) int  { return pushInt(f, int64(1)) }
+func doFconst0(f *frames.Frame, _ int64) int  { return pushFloat(f, int64(0)) }
+func doFconst1(f *frames.Frame, _ int64) int  { return pushFloat(f, int64(1)) }
+func doFconst2(f *frames.Frame, _ int64) int  { return pushFloat(f, int64(2)) }
+func doDconst0(f *frames.Frame, _ int64) int  { return pushFloat(f, int64(0)) }
+func doDconst1(f *frames.Frame, _ int64) int  { return pushFloat(f, int64(1)) }
+
+// the functions call by the dispatched functions
+func pushInt(f *frames.Frame, intToPush int64) int {
+	push(f, intToPush)
+	return 1
+}
+
+func pushFloat(f *frames.Frame, intToPush int64) int {
+	push(f, float64(intToPush))
+	return 1
+}
+
+func interpretBytecodes(bytecode int, f *frames.Frame) int {
+	PC := DispatchTable[bytecode](f, 0)
+	println("PC after call to DispatchTable[", bytecode, "] = ", PC)
+	return PC
+}