Fix "unsafe narrowing" warnings in absl, 4/n.

Addresses failures with the following, in some files:
-Wshorten-64-to-32
-Wimplicit-int-conversion
-Wsign-compare
-Wsign-conversion
-Wtautological-unsigned-zero-compare

(This specific CL focuses on .cc files in strings/, except /internal/.)

Bug: chromium:1292951
PiperOrigin-RevId: 468205572
Change-Id: Ifce3f1a7a4b2b2c359bf7700a11279bebfef8a15

Author: Abseil Team

absl/strings/ascii.cc

@@ -157,13 +157,13 @@ ABSL_DLL const char kToUpper[256] = {
 
 void AsciiStrToLower(std::string* s) {
   for (auto& ch : *s) {
-    ch = absl::ascii_tolower(ch);
+    ch = absl::ascii_tolower(static_cast<unsigned char>(ch));
   }
 }
 
 void AsciiStrToUpper(std::string* s) {
   for (auto& ch : *s) {
-    ch = absl::ascii_toupper(ch);
+    ch = absl::ascii_toupper(static_cast<unsigned char>(ch));
   }
 }
 
@@ -183,17 +183,17 @@ void RemoveExtraAsciiWhitespace(std::string* str) {
   for (; input_it < input_end; ++input_it) {
     if (is_ws) {
       // Consecutive whitespace?  Keep only the last.
-      is_ws = absl::ascii_isspace(*input_it);
+      is_ws = absl::ascii_isspace(static_cast<unsigned char>(*input_it));
       if (is_ws) --output_it;
     } else {
-      is_ws = absl::ascii_isspace(*input_it);
+      is_ws = absl::ascii_isspace(static_cast<unsigned char>(*input_it));
     }
 
     *output_it = *input_it;
     ++output_it;
   }
 
-  str->erase(output_it - &(*str)[0]);
+  str->erase(static_cast<size_t>(output_it - &(*str)[0]));
 }
 
 ABSL_NAMESPACE_END

absl/strings/charconv.cc

@@ -65,6 +65,8 @@ struct FloatTraits;
 
 template <>
 struct FloatTraits<double> {
+  using mantissa_t = uint64_t;
+
   // The number of mantissa bits in the given float type.  This includes the
   // implied high bit.
   static constexpr int kTargetMantissaBits = 53;
@@ -103,7 +105,7 @@ struct FloatTraits<double> {
   // a normal value is made, or it must be less narrow than that, in which case
   // `exponent` must be exactly kMinNormalExponent, and a subnormal value is
   // made.
-  static double Make(uint64_t mantissa, int exponent, bool sign) {
+  static double Make(mantissa_t mantissa, int exponent, bool sign) {
 #ifndef ABSL_BIT_PACK_FLOATS
     // Support ldexp no matter which namespace it's in.  Some platforms
     // incorrectly don't put it in namespace std.
@@ -116,8 +118,10 @@ struct FloatTraits<double> {
     if (mantissa > kMantissaMask) {
       // Normal value.
       // Adjust by 1023 for the exponent representation bias, and an additional
-      // 52 due to the implied decimal point in the IEEE mantissa represenation.
-      dbl += uint64_t{exponent + 1023u + kTargetMantissaBits - 1} << 52;
+      // 52 due to the implied decimal point in the IEEE mantissa
+      // representation.
+      dbl += static_cast<uint64_t>(exponent + 1023 + kTargetMantissaBits - 1)
+             << 52;
       mantissa &= kMantissaMask;
     } else {
       // subnormal value
@@ -134,16 +138,20 @@ struct FloatTraits<double> {
 // members and methods.
 template <>
 struct FloatTraits<float> {
+  using mantissa_t = uint32_t;
+
   static constexpr int kTargetMantissaBits = 24;
   static constexpr int kMaxExponent = 104;
   static constexpr int kMinNormalExponent = -149;
+
   static float MakeNan(const char* tagp) {
     // Support nanf no matter which namespace it's in.  Some platforms
     // incorrectly don't put it in namespace std.
     using namespace std;  // NOLINT
     return nanf(tagp);
   }
-  static float Make(uint32_t mantissa, int exponent, bool sign) {
+
+  static float Make(mantissa_t mantissa, int exponent, bool sign) {
 #ifndef ABSL_BIT_PACK_FLOATS
     // Support ldexpf no matter which namespace it's in.  Some platforms
     // incorrectly don't put it in namespace std.
@@ -157,7 +165,8 @@ struct FloatTraits<float> {
       // Normal value.
       // Adjust by 127 for the exponent representation bias, and an additional
       // 23 due to the implied decimal point in the IEEE mantissa represenation.
-      flt += uint32_t{exponent + 127u + kTargetMantissaBits - 1} << 23;
+      flt += static_cast<uint32_t>(exponent + 127 + kTargetMantissaBits - 1)
+             << 23;
       mantissa &= kMantissaMask;
     } else {
       // subnormal value
@@ -242,9 +251,9 @@ struct CalculatedFloat {
 
 // Returns the bit width of the given uint128.  (Equivalently, returns 128
 // minus the number of leading zero bits.)
-unsigned BitWidth(uint128 value) {
+int BitWidth(uint128 value) {
   if (Uint128High64(value) == 0) {
-    return static_cast<unsigned>(bit_width(Uint128Low64(value)));
+    return bit_width(Uint128Low64(value));
   }
   return 128 - countl_zero(Uint128High64(value));
 }
@@ -337,8 +346,10 @@ void EncodeResult(const CalculatedFloat& calculated, bool negative,
     *value = negative ? -0.0 : 0.0;
     return;
   }
-  *value = FloatTraits<FloatType>::Make(calculated.mantissa,
-                                        calculated.exponent, negative);
+  *value = FloatTraits<FloatType>::Make(
+      static_cast<typename FloatTraits<FloatType>::mantissa_t>(
+          calculated.mantissa),
+      calculated.exponent, negative);
 }
 
 // Returns the given uint128 shifted to the right by `shift` bits, and rounds
@@ -519,7 +530,7 @@ CalculatedFloat CalculateFromParsedHexadecimal(
     const strings_internal::ParsedFloat& parsed_hex) {
   uint64_t mantissa = parsed_hex.mantissa;
   int exponent = parsed_hex.exponent;
-  auto mantissa_width = static_cast<unsigned>(bit_width(mantissa));
+  int mantissa_width = bit_width(mantissa);
   const int shift = NormalizedShiftSize<FloatType>(mantissa_width, exponent);
   bool result_exact;
   exponent += shift;

absl/strings/cord.cc

@@ -20,6 +20,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <iomanip>
+#include <ios>
 #include <iostream>
 #include <limits>
 #include <ostream>
@@ -184,7 +185,7 @@ inline void Cord::InlineRep::reduce_size(size_t n) {
   assert(tag >= n);
   tag -= n;
   memset(data_.as_chars() + tag, 0, n);
-  set_inline_size(static_cast<char>(tag));
+  set_inline_size(tag);
 }
 
 inline void Cord::InlineRep::remove_prefix(size_t n) {
@@ -1098,7 +1099,7 @@ Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
                          : current_leaf_;
   const char* data = payload->IsExternal() ? payload->external()->base
                                            : payload->flat()->Data();
-  const size_t offset = current_chunk_.data() - data;
+  const size_t offset = static_cast<size_t>(current_chunk_.data() - data);
 
   auto* tree = CordRepSubstring::Substring(payload, offset, n);
   subcord.contents_.EmplaceTree(VerifyTree(tree), method);
@@ -1308,7 +1309,7 @@ static bool VerifyNode(CordRep* root, CordRep* start_node,
 
 std::ostream& operator<<(std::ostream& out, const Cord& cord) {
   for (absl::string_view chunk : cord.Chunks()) {
-    out.write(chunk.data(), chunk.size());
+    out.write(chunk.data(), static_cast<std::streamsize>(chunk.size()));
   }
   return out;
 }

absl/strings/cord_buffer.h

@@ -411,8 +411,12 @@ class CordBuffer {
 
   // Power2 functions
   static bool IsPow2(size_t size) { return absl::has_single_bit(size); }
-  static size_t Log2Floor(size_t size) { return absl::bit_width(size) - 1; }
-  static size_t Log2Ceil(size_t size) { return absl::bit_width(size - 1); }
+  static size_t Log2Floor(size_t size) {
+    return static_cast<size_t>(absl::bit_width(size) - 1);
+  }
+  static size_t Log2Ceil(size_t size) {
+    return static_cast<size_t>(absl::bit_width(size - 1));
+  }
 
   // Implementation of `CreateWithCustomLimit()`.
   // This implementation allows for future memory allocation hints to