commit f078fe1a0d31e50bcf095d4db5911822ec3edc0c
parent 5589e06adafcf33c598ec69026f45ef643350c3f
Author: Ryan Jeffrey <ryan@ryanmj.xyz>
Date: Sun, 12 Jun 2022 18:50:08 -0700
Fix conditional off-by-1, conditional constants, short source impl
Diffstat:
| M | src/decode.rs | | | 131 | ++++++++++++++++++++++++++++++++++++++++++++++++++++--------------------------- |
1 file changed, 87 insertions(+), 44 deletions(-)
diff --git a/src/decode.rs b/src/decode.rs
@@ -1,4 +1,5 @@
-// RISC-II decoder.
+// RISC-II decoder, the first stage in the pipeline. The next stages are
+// "execute" and then "commit".
// (C) Ryan Jeffrey <ryan@ryanmj.xyz>, 2022
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
@@ -16,40 +17,41 @@ extern crate core;
use core::convert::TryInto;
use std::fmt;
+use std::fmt::LowerHex;
/// Types of conditionals the RISC II supports.
#[derive(PartialEq, Eq, Copy, Clone)]
pub enum Conditional {
- /// Greater than.
- Gt,
- /// Less than or equal to.
- Le,
- /// Greater than or equal to.
- Ge,
- /// Less than.
- Lt,
- /// Higher than.
- Hi,
- /// Lower than or same.
- Los,
- /// Lower than no carry.
- Lonc,
- /// Higher than, carry.
- Hisc,
+ /// Greater than (signed >).
+ Gt = 1,
+ /// Less than or equal to (signed <=).
+ Le = 2,
+ /// Greater than or equal to (signed >=).
+ Ge = 3,
+ /// Less than (signed <).
+ Lt = 4,
+ /// Higher than (unsigned >).
+ Hi = 5,
+ /// Lower than or same (unsigned <=).
+ Los = 6,
+ /// Lower than no carry (unsigned <).
+ Lonc = 7,
+ /// Higher than, carry (unsigned >=).
+ Hisc = 8,
/// Plus (test sign).
- Pl,
+ Pl = 9,
/// Minus (test sign).
- Mi,
+ Mi = 10,
/// Not equal.
- Ne,
+ Ne = 11,
/// Equal.
- Eq,
+ Eq = 12,
/// No overflow (signed arithmetic).
- Nv,
+ Nv = 13,
/// Overflow (signed arithmetic).
- V,
+ V = 14,
/// Always (constant 1).
- Alw,
+ Alw = 15,
}
/// The 'source' of the instruction, which can either be a register name,
@@ -266,7 +268,7 @@ pub enum DecodeError {
/// return RISC-II conditional, or DecodeError if 0.
fn get_cond_from_opcode(opcode: u32) -> Result<Conditional, DecodeError> {
type C = Conditional;
- Ok(match (opcode & 0x780000) >> 18 {
+ Ok(match (opcode & 0x780000) >> 19 {
1 => C::Gt,
2 => C::Le,
3 => C::Ge,
@@ -311,7 +313,7 @@ pub fn decode(opcode: u32) -> Result<Instruction, DecodeError> {
let bottom_nibble = op & 0xf;
// Match the opcode's prefix.
- Ok(match op >> 5 {
+ Ok(match op >> 4 {
// Match the bottom four bytes of the opcode's prefix.
0 => match bottom_nibble {
0 => return Err(DecodeError::InvalidInstruction(0x0f, opcode)),
@@ -414,6 +416,57 @@ pub fn decode_file(file: &Vec<u8>, pos: usize) -> Result<(), DecodeError> {
// Impls.
+impl ShortSource {
+ pub fn new(opcode: u32, signed: bool) -> Self {
+ // Short source immediate-mode bottom 13 bits <12-0> or rs1 <4-0>.
+ if opcode & 0x2000 != 0 {
+ let mut tmp = Self::UImm13(opcode & 0x1fff);
+ if signed {
+ tmp.uimm_to_simm()
+ } else {
+ tmp
+ }
+ } else {
+ Self::Reg((opcode & 0x1f) as u8)
+ }
+ }
+
+ pub fn uimm_to_simm(&self) -> Self {
+ match *self {
+ Self::UImm13(u) => {
+ if u & 0x1000 != 0 {
+ // Sign-extend the 13 bit value to 32 bits.
+ Self::SImm13(-(u as i32))
+ } else {
+ Self::SImm13(u as i32)
+ }
+ }
+ Self::SImm13(s) => *self,
+ Self::Reg(r) => *self,
+ }
+ }
+}
+
+impl fmt::Display for ShortSource {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ match *self {
+ Self::Reg(r) => write!(f, "Reg {}", r),
+ Self::UImm13(u) => write!(f, "U{}", u),
+ Self::SImm13(i) => write!(f, "S{}", i),
+ }
+ }
+}
+
+impl LowerHex for ShortSource {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ match *self {
+ Self::Reg(r) => write!(f, "Register {:x}", r),
+ Self::UImm13(u) => write!(f, "(UImm) {:x}", u),
+ Self::SImm13(i) => write!(f, "(SImm) {:x}", i),
+ }
+ }
+}
+
impl fmt::Display for DecodeError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
@@ -438,8 +491,8 @@ impl fmt::Display for LongInstruction {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
- "Scc: {}, dest: {}, imm19: {}",
- self.scc, self.dest, self.imm19
+ "Scc: {}, dest: {}, imm19: 0x{:x} ({})",
+ self.scc, self.dest, self.imm19, self.imm19
)
}
}
@@ -458,8 +511,8 @@ impl fmt::Display for LongConditional {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
- "Scc: {}, cond: {}, imm19: {}",
- self.scc, self.dest, self.imm19
+ "Scc: {}, cond: {}, imm19: 0x{:x} ({})",
+ self.scc, self.dest, self.imm19, self.imm19
)
}
}
@@ -479,8 +532,8 @@ impl fmt::Display for ShortInstruction {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
- "Scc: {}, dest: {}, rs1: {}, short_source: {}",
- self.scc, self.dest, self.rs1, self.short_source
+ "Scc: {}, dest: {}, rs1: {}, short_source: 0x{:x} ({})",
+ self.scc, self.dest, self.rs1, self.short_source, self.short_source
)
}
}
@@ -500,22 +553,12 @@ impl fmt::Display for ShortConditional {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
- "Scc: {}, conditional: {}, rs1: {}, short_source: {}",
- self.scc, self.dest, self.rs1, self.short_source
+ "Scc: {}, conditional: {}, rs1: {}, short_source: 0x{:x} {}",
+ self.scc, self.dest, self.rs1, self.short_source, self.short_source
)
}
}
-impl fmt::Display for ShortSource {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- match *self {
- Self::Reg(r) => write!(f, "Reg {}", r),
- Self::UImm13(u) => write!(f, "U{}", u),
- Self::SImm13(i) => write!(f, "S{}", i),
- }
- }
-}
-
impl fmt::Display for Conditional {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match *self {
