From ab585c680b3222b01c1520ac33d1233ba1ba5036 Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Thu, 15 Oct 2020 10:16:20 +0200
Subject: [PATCH] stage1: Off-by-one error in int to float conversion

The base is 2^64 and not 2^64-1.

Closes #6683
---
 src/stage1/bigfloat.cpp       |  4 ++++
 test/stage1/behavior/cast.zig | 16 ++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/stage1/bigfloat.cpp b/src/stage1/bigfloat.cpp
index a2a3a3b69c..58b0aff54a 100644
--- a/src/stage1/bigfloat.cpp
+++ b/src/stage1/bigfloat.cpp
@@ -46,6 +46,10 @@ void bigfloat_init_bigint(BigFloat *dest, const BigInt *op) {
 
     float128_t base;
     ui64_to_f128M(UINT64_MAX, &base);
+    float128_t one_f128;
+    ui32_to_f128M(1, &one_f128);
+    f128M_add(&base, &one_f128, &base);
+
     const uint64_t *digits = bigint_ptr(op);
 
     for (size_t i = op->digit_count - 1;;) {
diff --git a/test/stage1/behavior/cast.zig b/test/stage1/behavior/cast.zig
index ce0d16d1a0..0eb00512b9 100644
--- a/test/stage1/behavior/cast.zig
+++ b/test/stage1/behavior/cast.zig
@@ -375,6 +375,22 @@ test "comptime_int @intToFloat" {
         expect(@TypeOf(result) == f32);
         expect(result == 1234.0);
     }
+    {
+        const result = @intToFloat(f64, 1234);
+        expect(@TypeOf(result) == f64);
+        expect(result == 1234.0);
+    }
+    {
+        const result = @intToFloat(f128, 1234);
+        expect(@TypeOf(result) == f128);
+        expect(result == 1234.0);
+    }
+    // big comptime_int (> 64 bits) to f128 conversion
+    {
+        const result = @intToFloat(f128, 0x1_0000_0000_0000_0000);
+        expect(@TypeOf(result) == f128);
+        expect(result == 0x1_0000_0000_0000_0000.0);
+    }
 }
 
 test "@intCast i32 to u7" {