[libc-commits] [libc] [libc][bit_test] fix -Wimplicit-int-conversion (PR #126317)

[Nick Desaulniers via libc-commits]

https://github.com/nickdesaulniers created https://github.com/llvm/llvm-project/pull/126317

Fixes:

    llvm-project/libc/src/__support/CPP/bit.h:235:28: error: implicit
    conversion loses integer precision: 'int' to
    'cpp::enable_if_t<cpp::is_unsigned_v<unsigned short>, unsigned short>' (aka
    'unsigned short') [-Werror,-Wimplicit-int-conversion]
      235 |   return (value << rotate) | (value >> (N - rotate));
          |   ~~~~~~ ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
    llvm-project/libc/src/__support/CPP/bit.h:247:28: error: implicit
    conversion loses integer precision: 'int' to
    'cpp::enable_if_t<cpp::is_unsigned_v<unsigned short>, unsigned short>' (aka
    'unsigned short') [-Werror,-Wimplicit-int-conversion]
      247 |   return (value >> rotate) | (value << (N - rotate));
          |   ~~~~~~ ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
    llvm-project/libc/test/src/__support/CPP/bit_test.cpp:45:36: error:
    implicit conversion loses integer precision: 'int' to 'unsigned char'
    [-Werror,-Wimplicit-int-conversion]
       45 |     EXPECT_FALSE(has_single_bit<T>(two_bits_value));
          |                  ~~~~~~~~~~~~~~    ^~~~~~~~~~~~~~

Via the libc-cpp-utils-tests ninja target.


>From b50a2cc19bef10879cd1708e72a390634a484f5a Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Fri, 7 Feb 2025 14:01:12 -0800
Subject: [PATCH] [libc][bit_test] fix -Wimplicit-int-conversion

Fixes:

    llvm-project/libc/src/__support/CPP/bit.h:235:28: error: implicit
    conversion loses integer precision: 'int' to
    'cpp::enable_if_t<cpp::is_unsigned_v<unsigned short>, unsigned short>' (aka
    'unsigned short') [-Werror,-Wimplicit-int-conversion]
      235 |   return (value << rotate) | (value >> (N - rotate));
          |   ~~~~~~ ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
    llvm-project/libc/src/__support/CPP/bit.h:247:28: error: implicit
    conversion loses integer precision: 'int' to
    'cpp::enable_if_t<cpp::is_unsigned_v<unsigned short>, unsigned short>' (aka
    'unsigned short') [-Werror,-Wimplicit-int-conversion]
      247 |   return (value >> rotate) | (value << (N - rotate));
          |   ~~~~~~ ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
    llvm-project/libc/test/src/__support/CPP/bit_test.cpp:45:36: error:
    implicit conversion loses integer precision: 'int' to 'unsigned char'
    [-Werror,-Wimplicit-int-conversion]
       45 |     EXPECT_FALSE(has_single_bit<T>(two_bits_value));
          |                  ~~~~~~~~~~~~~~    ^~~~~~~~~~~~~~

Via the libc-cpp-utils-tests ninja target.
---
 libc/src/__support/CPP/bit.h             | 4 ++--
 libc/test/src/__support/CPP/bit_test.cpp | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index adcd0472747d01a..82b9eb51282625a 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -232,7 +232,7 @@ rotl(T value, int rotate) {
     return value;
   if (rotate < 0)
     return cpp::rotr<T>(value, -rotate);
-  return (value << rotate) | (value >> (N - rotate));
+  return static_cast<T>((value << rotate) | (value >> (N - rotate)));
 }
 
 template <typename T>
@@ -244,7 +244,7 @@ rotr(T value, int rotate) {
     return value;
   if (rotate < 0)
     return cpp::rotl<T>(value, -rotate);
-  return (value >> rotate) | (value << (N - rotate));
+  return static_cast<T>((value >> rotate) | (value << (N - rotate)));
 }
 
 // TODO: Do we need this function at all? How is it different from
diff --git a/libc/test/src/__support/CPP/bit_test.cpp b/libc/test/src/__support/CPP/bit_test.cpp
index 9429b66ad1f9815..1f2315281bc1dab 100644
--- a/libc/test/src/__support/CPP/bit_test.cpp
+++ b/libc/test/src/__support/CPP/bit_test.cpp
@@ -41,7 +41,8 @@ TYPED_TEST(LlvmLibcBitTest, HasSingleBit, UnsignedTypes) {
   constexpr auto LSB = T(1);
   constexpr auto MSB = T(~(ALL_ONES >> 1));
   for (T value = 1; value; value <<= 1) {
-    auto two_bits_value = value | ((value <= MIDPOINT) ? MSB : LSB);
+    T two_bits_value =
+        static_cast<T>(value | ((value <= MIDPOINT) ? MSB : LSB));
     EXPECT_FALSE(has_single_bit<T>(two_bits_value));
   }
 }