From dd2ac10ab9ed9548acb8ffc879e522ea1f47fbbb Mon Sep 17 00:00:00 2001
From: Jared Ramirez <jaredramirez@hey.com>
Date: Tue, 15 Jun 2021 19:19:03 -0700
Subject: [PATCH] Add RocDec.sub

---
 .gitignore                            |  1 +
 compiler/builtins/bitcode/src/dec.zig | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/.gitignore b/.gitignore
index 242dbec6f8..d0ccfa7943 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,6 +14,7 @@ vgcore.*
 #editors
 .idea/
 .vscode/
+.ignore
 
 #files too big to track in git
 editor/benches/resources/100000_lines.roc
diff --git a/compiler/builtins/bitcode/src/dec.zig b/compiler/builtins/bitcode/src/dec.zig
index 1fdf363910..d194e3e333 100644
--- a/compiler/builtins/bitcode/src/dec.zig
+++ b/compiler/builtins/bitcode/src/dec.zig
@@ -213,6 +213,17 @@ pub const RocDec = struct {
         }
     }
 
+    pub fn sub(self: RocDec, other: RocDec) RocDec {
+        var answer: i128 = undefined;
+        const overflowed = @subWithOverflow(i128, self.num, other.num, &answer);
+
+        if (!overflowed) {
+            return RocDec{ .num = answer };
+        } else {
+            std.debug.panic("TODO runtime exception for overflow!", .{});
+        }
+    }
+
     pub fn mul(self: RocDec, other: RocDec) RocDec {
         const self_i128 = self.num;
         const other_i128 = other.num;
@@ -652,6 +663,18 @@ test "add: 1" {
     try expectEqual(RocDec{ .num = 1 }, dec.add(.{ .num = 1 }));
 }
 
+test "sub: 0" {
+    var dec: RocDec = .{ .num = 1 };
+
+    try expectEqual(RocDec{ .num = 1 }, dec.sub(.{ .num = 0 }));
+}
+
+test "sub: 1" {
+    var dec: RocDec = .{ .num = 1 };
+
+    try expectEqual(RocDec{ .num = 0 }, dec.sub(.{ .num = 1 }));
+}
+
 test "mul: by 0" {
     var dec: RocDec = .{ .num = 0 };