From 0059b389aee7519ec308bc5c9fff8f874c830fdb Mon Sep 17 00:00:00 2001
From: ychenfo <yc@m-labs.hk>
Date: Sat, 2 Apr 2022 03:26:15 +0800
Subject: [PATCH] nac3core: fix powi with negative integer power

---
 nac3core/src/codegen/expr.rs | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/nac3core/src/codegen/expr.rs b/nac3core/src/codegen/expr.rs
index 33c0eec4e..5e7f5b24c 100644
--- a/nac3core/src/codegen/expr.rs
+++ b/nac3core/src/codegen/expr.rs
@@ -957,10 +957,36 @@ pub fn gen_binop_expr<'ctx, 'a, G: CodeGenerator>(
             ctx.module.add_function("llvm.powi.f64.i16", ty, None)
         });
         let right = ctx.builder.build_int_truncate(right.into_int_value(), i16_t, "r_pow");
-        ctx.builder
+        let is_neg = ctx.builder.build_int_compare(
+            inkwell::IntPredicate::SLT,
+            right,
+            i16_t.const_zero(),
+            "powi_pow_neg",
+        );
+        let abs_intr = ctx.module.get_function("llvm.abs.i16").unwrap_or_else(|| {
+            let ty = i16_t.fn_type(&[i16_t.into(), ctx.ctx.bool_type().into()], false);
+            ctx.module.add_function("llvm.abs.i16", ty, None)
+        });
+        let right = ctx
+            .builder
+            .build_call(
+                abs_intr,
+                &[right.into(), ctx.ctx.bool_type().const_int(0, false).into()],
+                "pow_abs",
+            )
+            .try_as_basic_value()
+            .unwrap_left();
+        let pow = ctx
+            .builder
             .build_call(pow_intr, &[left.into(), right.into()], "f_pow_i")
             .try_as_basic_value()
-            .unwrap_left()
+            .unwrap_left();
+        let reciprocal = ctx.builder.build_float_div(
+            ctx.ctx.f64_type().const_float(1.0),
+            pow.into_float_value(),
+            "recip",
+        );
+        ctx.builder.build_select(is_neg, reciprocal, pow.into_float_value(), "float_pow_i")
     } else {
         unimplemented!()
     }