From 93b2544ab446ebc63bedd5d05c373eb1c28ddafa Mon Sep 17 00:00:00 2001
From: Jimmy Lu <jimmylu@meta.com>
Date: Thu, 29 Feb 2024 10:23:28 -0800
Subject: [PATCH] Safer JSON cast from floating point to integer across
 platforms

Summary:
https://github.com/facebookincubator/velox/pull/8899

When casting from floating point to integer, first cast losslessly into `double`, then check if it can be cast into `int64_t` using boundaries from `folly::constexpr_clamp_cast`, if it fits then we do another integer to integer cast which is trivial.

Reviewed By: bikramSingh91

Differential Revision: D54313505

fbshipit-source-id: 7ad5cf182fe3ac8b304679b7e95eff21cee51d00
---
 velox/functions/prestosql/types/JsonType.cpp | 24 +++++++++++++++-----
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/velox/functions/prestosql/types/JsonType.cpp b/velox/functions/prestosql/types/JsonType.cpp
index 9defbf9c7c98..7b11b8f9eaa1 100644
--- a/velox/functions/prestosql/types/JsonType.cpp
+++ b/velox/functions/prestosql/types/JsonType.cpp
@@ -569,16 +569,28 @@ simdjson::simdjson_result<T> fromString(const std::string_view& s) {
 template <typename To, typename From>
 simdjson::error_code convertIfInRange(From x, exec::GenericWriter& writer) {
   static_assert(std::is_signed_v<From> && std::is_signed_v<To>);
-  static_assert(std::is_integral_v<To> || !std::is_integral_v<From>);
-  if constexpr (!std::is_same_v<To, From>) {
-    constexpr From kMin = std::numeric_limits<To>::lowest();
-    constexpr From kMax = std::numeric_limits<To>::max();
+  if constexpr (std::is_integral_v<To> == std::is_integral_v<From>) {
+    if constexpr (sizeof(To) < sizeof(From)) {
+      constexpr From kMin = std::numeric_limits<To>::lowest();
+      constexpr From kMax = std::numeric_limits<To>::max();
+      if (!(kMin <= x && x <= kMax)) {
+        return simdjson::NUMBER_OUT_OF_RANGE;
+      }
+    }
+    writer.castTo<To>() = x;
+    return simdjson::SUCCESS;
+  } else {
+    static_assert(std::is_integral_v<To> && !std::is_integral_v<From>);
+    // Upper/lower bound values that could be accurately represented in both
+    // int64_t and double types.  Same values are used by
+    // folly::constexpr_clamp_cast.
+    constexpr double kMin = -9223372036854774784.0;
+    constexpr double kMax = 9223372036854774784.0;
     if (!(kMin <= x && x <= kMax)) {
       return simdjson::NUMBER_OUT_OF_RANGE;
     }
+    return convertIfInRange<To, int64_t>(x, writer);
   }
-  writer.castTo<To>() = x;
-  return simdjson::SUCCESS;
 }
 
 template <TypeKind kind>