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kissa.bsky.social

@kissa.bsky.social

Tomfoolery, nincompoopery, programming

37 followers374 following39 posts

kissa.bsky.socialOct 19, 2023 9:11am

Here's the whole set of immediate instructions. This makes me reconsider the design, not only because of the effort of testing all of that stuff but also because I don't want to type "SHLAB" when I just want to do a 1-bit left shift. Maybe it's time to write some programs first and reconsider this.

Previous picture, plus new stuff (8-bit immediate instructions)

// If bit 6 (immediate mode) is set, bit 7 sets "byte mode"
//
// Instruction names are postfixed with "b" for immediate.
// Arithmetic instructions with 8-bit immediate operand (96-111):
//
// addb op1, op2, imm8 ; op1 <- op2 + imm8 01100000
// subb
// mulb
// divb
// modb
// andb
// orb
// xorb
// shlb
// shrb
// add1b
// sub1b
// movb
//
// // Arithmetic instructions with 8-bit immediate operand, augmented assignment
// (112-127):
//
// addab op1, imm8 ; op1 <- op2 + imm8 01110000
// subab
// mulab
// divab
// modab
// andab
// orab
// xorab
// shlab
// shrab
// incab
// decab
// nopab

kissa.bsky.socialOct 19, 2023 8:15pm

Actually need to implement a bunch of arithmetic instructions and test them somehow efficiently. Here's a start.

List of test instructions that ChatGPT wrote me.

export const opcodes: { [key: number]: string } = {
0b00000000: "add", // add <op1> <op2> <op3> - op1 <- op2 + op3
0b00000001: "sub", // sub <op1> <op2> <op3> - op1 <- op2 - op3
0b00000010: "mul", // mul <op1> <op2> <op3> - op1 <- op2 * op3
// etc, ending with 0b00001100: "mov"

0b00010000: "adda", // add <op1> <op2> - op1 <- op1 + op2
0b00010001: "suba", // sub <op1> <op2> - op1 <- op1 - op2
0b00010010: "mula", // mul <op1> <op2> - op1 <- op1 * op2
// etc, ending with 0b00011100: "nop"

0b11110000: "hlt", // hlt <?> <?> <?> - halt program execution
0b11110001: "hcf", // hcf <?> <?> <?> - halt and catch fire
}

Implementation of first 3 arithmetic instructions:

if (instr === "add") {
writeOperand(op1, op2value + op3value)
}
if (instr === "sub") {
writeOperand(op1, op2value - op3value)
}
if (instr === "mul") {
writeOperand(op1, op2value * op3value)
}
if (instr === "hlt") {
return false
}
if (instr === "hcf") {
error("Machine caught fire")
}
return true

test("arithmetic instructions", () => {
testArithmetic(instr.add, 0x1234, 0x2345, 0x3579)
testArithmetic(instr.sub, 0x4131, 0x2121, 0x2010)
testArithmetic(instr.mul, 111, 20, 2220)
testArithmetic(instr.mul, -111, 20, -2220)
testArithmetic(instr.mul, -1, -0x7fff, 0x7fff)
// TODO should overflow probably
// testArithmetic(instr.mul, -1, -0x8000, -0x8000)
})

kissa.bsky.social

@kissa.bsky.social

Tomfoolery, nincompoopery, programming

37 followers374 following39 posts

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