From 8b7558a31bd06d815b138661be0af543cd596ec5 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 22 Jul 2025 02:43:20 -0400
Subject: oemu: cpu: Introduce decoding logic for DIV

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 usr.bin/oemu/cpu.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

(limited to 'usr.bin/oemu')

diff --git a/usr.bin/oemu/cpu.c b/usr.bin/oemu/cpu.c
index ccac0b1..5689953 100644
--- a/usr.bin/oemu/cpu.c
+++ b/usr.bin/oemu/cpu.c
@@ -168,6 +168,35 @@ cpu_mul(struct oemu_cpu *cpu, inst_t *inst)
         imm, inst->imm, inst->rd, regs->xreg[inst->rd]);
 }
 
+/*
+ * Decode the INST_DIV instruction
+ *
+ * @cpu: CPU that is executing
+ * @inst: Instruction dword
+ */
+static void
+cpu_div(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 'div'\n");
+        return;
+    }
+
+    imm = regs->xreg[inst->rd];
+    if (imm == 0) {
+        /* TODO: Some sort of interrupt */
+        printf("** DIVIDE BY ZERO **\n");
+        return;
+    }
+
+    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
  */
@@ -213,6 +242,9 @@ cpu_kick(struct oemu_cpu *cpu, struct sysmem *mem)
         case INST_MUL:
             cpu_mul(cpu, inst);
             break;
+        case INST_DIV:
+            cpu_div(cpu, inst);
+            break;
         }
 
         /* Is this a halt instruction? */
-- 
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