From 0341c0f9dd3c03cc4cde1f070f739173f80f852d Mon Sep 17 00:00:00 2001
From: Richard Feldman <oss@rtfeldman.com>
Date: Sat, 15 May 2021 14:59:16 -0400
Subject: [PATCH] Beginnings of RocDec in Zig

---
 compiler/builtins/bitcode/src/dec.zig | 58 +++++++++++++++++++++++++++
 compiler/builtins/bitcode/src/num.zig |  1 +
 2 files changed, 59 insertions(+)
 create mode 100644 compiler/builtins/bitcode/src/dec.zig

diff --git a/compiler/builtins/bitcode/src/dec.zig b/compiler/builtins/bitcode/src/dec.zig
new file mode 100644
index 0000000000..99522031d5
--- /dev/null
+++ b/compiler/builtins/bitcode/src/dec.zig
@@ -0,0 +1,58 @@
+const std = @import("std");
+
+pub const RocDec = struct {
+    num: i128,
+
+    pub fn add(self: RocDec, other: RocDec) RocDec {
+        var answer: i128 = undefined;
+        const overflowed = @addWithOverflow(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_i256 = @intCast(i256, self.num);
+        const other_i256 = @intCast(i256, other.num);
+        const answer = 0; //self_i256 * other_i256;
+
+        if ((answer >> 192) < 0) {
+            return RocDec{ .num = 0 };
+            // return RocDec{ .num = @intCast(i128, @divTrunc(answer, one_e20)) };
+        } else {
+            return RocDec{ .num = 0 };
+           // std.debug.panic("TODO runtime exception for overflow!", .{});
+        }
+    }
+};
+
+const one_e20: i256 = 100000000000000000000;
+
+const expectEqual = std.testing.expectEqual;
+
+test "add" {
+    expectEqual(
+        RocDec { .num = 0 },
+        (RocDec{ .num = 0 }).add(RocDec{ .num = 0 })
+    );
+}
+
+test "mul" {
+    expectEqual(
+        RocDec { .num = 0 },
+        (RocDec{ .num = 0 }).mul(RocDec{ .num = 0 })
+    );
+
+    expectEqual(
+        RocDec { .num = 100000000000000000000 },
+        (RocDec{ .num = 100000000000000000000 }).mul(RocDec{ .num = 100000000000000000000 })
+    );
+
+    // expectEqual(
+    //     (RocDec{ .num = 1 }).add(RocDec{ .num = 1 }),
+    //     RocDec { .num = 0 }
+    // );
+}
diff --git a/compiler/builtins/bitcode/src/num.zig b/compiler/builtins/bitcode/src/num.zig
index b42aee20ca..4051ae4de4 100644
--- a/compiler/builtins/bitcode/src/num.zig
+++ b/compiler/builtins/bitcode/src/num.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const dec = @import("dec");
 const always_inline = std.builtin.CallOptions.Modifier.always_inline;
 const math = std.math;