From f6bf24b2f3e1d65ce66625c4466aa2af9edff41c Mon Sep 17 00:00:00 2001
From: Robin Voetter <robin@voetter.nl>
Date: Sat, 16 Oct 2021 00:13:33 +0200
Subject: stage2: comptime saturating shl

---
 src/value.zig | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

(limited to 'src/value.zig')

diff --git a/src/value.zig b/src/value.zig
index 264525a204..127c6c27b4 100644
--- a/src/value.zig
+++ b/src/value.zig
@@ -2404,6 +2404,39 @@ pub const Value = extern union {
         }
     }
 
+    pub fn shlSat(
+        lhs: Value,
+        rhs: Value,
+        ty: Type,
+        arena: *Allocator,
+        target: Target,
+    ) !Value {
+        // TODO is this a performance issue? maybe we should try the operation without
+        // resorting to BigInt first.
+        const info = ty.intInfo(target);
+
+        var lhs_space: Value.BigIntSpace = undefined;
+        const lhs_bigint = lhs.toBigInt(&lhs_space);
+        const shift = rhs.toUnsignedInt();
+        const limbs = try arena.alloc(
+            std.math.big.Limb,
+            std.math.big.int.calcTwosCompLimbCount(info.bits),
+        );
+        var result_bigint = BigIntMutable{
+            .limbs = limbs,
+            .positive = undefined,
+            .len = undefined,
+        };
+        result_bigint.shiftLeftSat(lhs_bigint, shift, info.signedness, info.bits);
+        const result_limbs = result_bigint.limbs[0..result_bigint.len];
+
+        if (result_bigint.positive) {
+            return Value.Tag.int_big_positive.create(arena, result_limbs);
+        } else {
+            return Value.Tag.int_big_negative.create(arena, result_limbs);
+        }
+    }
+
     pub fn shr(lhs: Value, rhs: Value, allocator: *Allocator) !Value {
         // TODO is this a performance issue? maybe we should try the operation without
         // resorting to BigInt first.
-- 
cgit v1.2.3