From af93dd2857940d2f0a19481f37ccdb25656ae15d Mon Sep 17 00:00:00 2001 From: Ian Moffett Date: Tue, 22 Jul 2025 01:39:53 -0400 Subject: oemu: cpu: Introduce decoding logic for SUB Signed-off-by: Ian Moffett --- usr.bin/oemu/cpu.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'usr.bin') diff --git a/usr.bin/oemu/cpu.c b/usr.bin/oemu/cpu.c index 8ec106a..84f04bf 100644 --- a/usr.bin/oemu/cpu.c +++ b/usr.bin/oemu/cpu.c @@ -122,6 +122,29 @@ cpu_add(struct oemu_cpu *cpu, inst_t *inst) imm, inst->imm, inst->rd, regs->xreg[inst->rd]); } +/* + * Decode the INST_SUB instruction + * + * @cpu: CPU that is executing + * @inst: Instruction dword + */ +static void +cpu_sub(struct oemu_cpu *cpu, inst_t *inst) +{ + struct cpu_regs *regs = &cpu->regs; + imm_t imm; + + if (inst->rd > NELEM(regs->xreg)) { + printf("bad register operand for 'sub'\n"); + return; + } + + imm = regs->xreg[inst->rd]; + regs->xreg[inst->rd] -= inst->imm; + printf("%d - %d -> X%d, new=%d\n", + imm, inst->imm, inst->rd, regs->xreg[inst->rd]); +} + /* * Reset a CPU to a default state */ @@ -161,6 +184,9 @@ cpu_kick(struct oemu_cpu *cpu, struct sysmem *mem) case INST_ADD: cpu_add(cpu, inst); break; + case INST_SUB: + cpu_sub(cpu, inst); + break; } /* Is this a halt instruction? */ -- cgit v1.2.3