--- pdfium.old/core/fpdfapi/page/cpdf_pageobjectholder_unittest.cpp
+++ pdfium/core/fpdfapi/page/cpdf_pageobjectholder_unittest.cpp
@@ -40,7 +40,7 @@
   EXPECT_EQ(data[0], fMin);
   EXPECT_EQ(data[1], fMax);
   EXPECT_EQ(data[2], fInf);
-  EXPECT_EQ(isnan(data[3]), isnan(fNan));
+  EXPECT_EQ(std::isnan(data[3]), std::isnan(fNan));
 
   std::map<GraphicsData, int> graphics_map;
 
--- pdfium.old/core/fpdfapi/page/cpdf_psengine.cpp
+++ pdfium/core/fpdfapi/page/cpdf_psengine.cpp
@@ -75,7 +75,7 @@
 // Round half up is a nearest integer round with half-way numbers always rounded
 // up. Example: -5.5 rounds to -5.
 float RoundHalfUp(float f) {
-  if (isnan(f)) {
+  if (std::isnan(f)) {
     return 0;
   }
   if (f > std::numeric_limits<float>::max() - 0.5f) {
--- pdfium.old/core/fxcrt/css/cfx_cssdeclaration.cpp
+++ pdfium/core/fxcrt/css/cfx_cssdeclaration.cpp
@@ -37,7 +37,7 @@
 
   size_t nUsedLen = 0;
   float value = FXSYS_wcstof(view, &nUsedLen);
-  if (nUsedLen == 0 || !isfinite(value)) {
+  if (nUsedLen == 0 || !std::isfinite(value)) {
     return std::nullopt;
   }
   view = view.Substr(nUsedLen);
--- pdfium.old/core/fxcrt/fx_extension.h
+++ pdfium/core/fxcrt/fx_extension.h
@@ -131,17 +131,17 @@
 // All NaNs are treated as equal to each other and greater than infinity.
 template <typename T>
 bool FXSYS_SafeEQ(const T& lhs, const T& rhs) {
-  return (isnan(lhs) && isnan(rhs)) ||
-         (!isnan(lhs) && !isnan(rhs) && lhs == rhs);
+  return (std::isnan(lhs) && std::isnan(rhs)) ||
+         (!std::isnan(lhs) && !std::isnan(rhs) && lhs == rhs);
 }
 
 template <typename T>
 bool FXSYS_SafeLT(const T& lhs, const T& rhs) {
-  if (isnan(lhs) && isnan(rhs)) {
+  if (std::isnan(lhs) && std::isnan(rhs)) {
     return false;
   }
-  if (isnan(lhs) || isnan(rhs)) {
-    return isnan(lhs) < isnan(rhs);
+  if (std::isnan(lhs) || std::isnan(rhs)) {
+    return std::isnan(lhs) < std::isnan(rhs);
   }
   return lhs < rhs;
 }
--- pdfium.old/core/fxcrt/fx_system.cpp
+++ pdfium/core/fxcrt/fx_system.cpp
@@ -99,7 +99,7 @@
 }  // namespace
 
 int FXSYS_roundf(float f) {
-  if (isnan(f)) {
+  if (std::isnan(f)) {
     return 0;
   }
   if (f < static_cast<float>(std::numeric_limits<int>::min())) {
@@ -112,7 +112,7 @@
 }
 
 int FXSYS_round(double d) {
-  if (isnan(d)) {
+  if (std::isnan(d)) {
     return 0;
   }
   if (d < static_cast<double>(std::numeric_limits<int>::min())) {
--- pdfium.old/fxjs/cfx_v8_unittest.cpp
+++ pdfium/fxjs/cfx_v8_unittest.cpp
@@ -88,7 +88,7 @@
   auto undef = cfx_v8()->NewUndefined();
   EXPECT_FALSE(cfx_v8()->ToBoolean(undef));
   EXPECT_EQ(0, cfx_v8()->ToInt32(undef));
-  EXPECT_TRUE(isnan(cfx_v8()->ToDouble(undef)));
+  EXPECT_TRUE(std::isnan(cfx_v8()->ToDouble(undef)));
   EXPECT_EQ("undefined", cfx_v8()->ToByteString(undef));
   EXPECT_EQ(L"undefined", cfx_v8()->ToWideString(undef));
   EXPECT_TRUE(cfx_v8()->ToObject(undef).IsEmpty());
--- pdfium.old/fxjs/cjs_publicmethods.cpp
+++ pdfium/fxjs/cjs_publicmethods.cpp
@@ -459,7 +459,7 @@
 
   if (status == fxjs::ConversionStatus::kBadDate) {
     dRet = JS_DateParse(isolate, value);
-    if (!isnan(dRet)) {
+    if (!std::isnan(dRet)) {
       return dRet;
     }
   }
@@ -951,7 +951,7 @@
                                  nullptr);
   }
 
-  if (isnan(dDate)) {
+  if (std::isnan(dDate)) {
     WideString swMsg = WideString::Format(
         JSGetStringFromID(JSMessage::kParseDateError).c_str(), sFormat.c_str());
     AlertIfPossible(pEvent, WideString::FromASCII("AFDate_FormatEx"), swMsg);
@@ -994,7 +994,7 @@
   int nYear = StringToFloat(wsArray[7].AsStringView());
   double dRet = FX_MakeDate(FX_MakeDay(nYear, nMonth - 1, nDay),
                             FX_MakeTime(nHour, nMin, nSec, 0));
-  if (isnan(dRet)) {
+  if (std::isnan(dRet)) {
     dRet = JS_DateParse(isolate, strValue);
   }
 
@@ -1028,7 +1028,7 @@
   WideString sFormat = pRuntime->ToWideString(params[0]);
   double dRet = ParseDateUsingFormat(pRuntime->GetIsolate(), strValue, sFormat,
                                      &bWrongFormat);
-  if (bWrongFormat || isnan(dRet)) {
+  if (bWrongFormat || std::isnan(dRet)) {
     WideString swMsg = WideString::Format(
         JSGetStringFromID(JSMessage::kParseDateError).c_str(), sFormat.c_str());
     AlertIfPossible(pEvent, WideString::FromASCII("AFDate_KeystrokeEx"), swMsg);
@@ -1306,7 +1306,7 @@
   WideString sFormat = pRuntime->ToWideString(params[1]);
   double dDate =
       ParseDateUsingFormat(pRuntime->GetIsolate(), sValue, sFormat, nullptr);
-  if (isnan(dDate)) {
+  if (std::isnan(dDate)) {
     WideString swMsg = WideString::Format(
         JSGetStringFromID(JSMessage::kParseDateError).c_str(), sFormat.c_str());
     AlertIfPossible(pRuntime->GetCurrentEventContext(),
@@ -1326,7 +1326,7 @@
   WideString sFunction = pRuntime->ToWideString(params[0]);
   double arg1 = pRuntime->ToDouble(params[1]);
   double arg2 = pRuntime->ToDouble(params[2]);
-  if (isnan(arg1) || isnan(arg2)) {
+  if (std::isnan(arg1) || std::isnan(arg2)) {
     return CJS_Result::Failure(JSMessage::kValueError);
   }
 
--- pdfium.old/fxjs/cjs_runtime.cpp
+++ pdfium/fxjs/cjs_runtime.cpp
@@ -236,7 +236,7 @@
   }
 
   v8::Local<v8::Number> num = maybeNum.ToLocalChecked();
-  if (isnan(num->Value()) && !bAllowNaN) {
+  if (std::isnan(num->Value()) && !bAllowNaN) {
     return value;
   }
 
--- pdfium.old/fxjs/cjs_util.cpp
+++ pdfium/fxjs/cjs_util.cpp
@@ -177,7 +177,7 @@
   }
 
   v8::Local<v8::Date> v8_date = params[1].As<v8::Date>();
-  if (v8_date.IsEmpty() || isnan(pRuntime->ToDouble(v8_date))) {
+  if (v8_date.IsEmpty() || std::isnan(pRuntime->ToDouble(v8_date))) {
     return CJS_Result::Failure(JSMessage::kSecondParamInvalidDateError);
   }
 
@@ -393,7 +393,7 @@
     dDate = CJS_PublicMethods::ParseDateUsingFormat(pRuntime->GetIsolate(),
                                                     sDate, sFormat, nullptr);
   }
-  if (isnan(dDate)) {
+  if (std::isnan(dDate)) {
     return CJS_Result::Success(pRuntime->NewUndefined());
   }
 
--- pdfium.old/fxjs/fx_date_helpers.cpp
+++ pdfium/fxjs/fx_date_helpers.cpp
@@ -278,7 +278,7 @@
 }
 
 double FX_MakeDate(double day, double time) {
-  if (!isfinite(day) || !isfinite(time)) {
+  if (!std::isfinite(day) || !std::isfinite(time)) {
     return nan("");
   }
 
@@ -565,7 +565,7 @@
 
   dt = FX_MakeDate(FX_MakeDay(nYear, nMonth - 1, nDay),
                    FX_MakeTime(nHour, nMin, nSec, 0));
-  if (isnan(dt)) {
+  if (std::isnan(dt)) {
     return ConversionStatus::kBadDate;
   }
 
--- pdfium.old/fxjs/js_define.cpp
+++ pdfium/fxjs/js_define.cpp
@@ -59,7 +59,7 @@
   }
 
   double date = value.As<v8::Number>()->Value();
-  return isfinite(date) ? FX_LocalTime(date) : date;
+  return std::isfinite(date) ? FX_LocalTime(date) : date;
 }
 
 v8::LocalVector<v8::Value> ExpandKeywordParams(
--- pdfium.old/fxjs/xfa/cfxjse_formcalc_context.cpp
+++ pdfium/fxjs/xfa/cfxjse_formcalc_context.cpp
@@ -4267,7 +4267,7 @@
     bsLocale = ValueToUTF8String(info.GetIsolate(), localeValue);
   }
 
-  if (isnan(fNumber) || fNumber < 0.0f || fNumber > 922337203685477550.0f) {
+  if (std::isnan(fNumber) || fNumber < 0.0f || fNumber > 922337203685477550.0f) {
     info.GetReturnValue().Set(fxv8::NewStringHelper(info.GetIsolate(), "*"));
     return;
   }
--- pdfium.old/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
+++ pdfium/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
@@ -90,7 +90,7 @@
     CFXJSE_ScopeUtil_IsolateHandleContext scope(GetJseContext());
     v8::Local<v8::Value> value = GetValue();
     EXPECT_TRUE(fxv8::IsNumber(value));
-    EXPECT_TRUE(isnan(fxv8::ReentrantToDoubleHelper(isolate(), value)));
+    EXPECT_TRUE(std::isnan(fxv8::ReentrantToDoubleHelper(isolate(), value)));
   }
 
   void ExecuteExpectString(ByteStringView input, const char* expected) {
--- pdfium.old/third_party/fast_float/src/tests/basictest.cpp
+++ pdfium/third_party/fast_float/src/tests/basictest.cpp
@@ -741,12 +741,12 @@
     return std::copysign(x, y);
   };
 
-  auto isnan = [](double x) -> bool { return x != x; };
+  auto std::isnan = [](double x) -> bool { return x != x; };
 
   FASTFLOAT_CHECK_EQ(result.ec, expected_ec);
   FASTFLOAT_CHECK_EQ(result.ptr, str.data() + str.size());
   FASTFLOAT_CHECK_EQ(copysign(1, actual), copysign(1, expected));
-  FASTFLOAT_CHECK_EQ(isnan(actual), isnan(expected));
+  FASTFLOAT_CHECK_EQ(std::isnan(actual), std::isnan(expected));
   FASTFLOAT_CHECK_EQ(actual, expected);
 
 #undef FASTFLOAT_CHECK_EQ
--- pdfium.old/third_party/lcms/src/cmsintrp.c
+++ pdfium/third_party/lcms/src/cmsintrp.c
@@ -223,7 +223,7 @@
 // To prevent out of bounds indexing
 cmsINLINE cmsFloat32Number fclamp(cmsFloat32Number v) 
 {
-    return ((v < 1.0e-9f) || isnan(v)) ? 0.0f : (v > 1.0f ? 1.0f : v);
+    return ((v < 1.0e-9f) || std::isnan(v)) ? 0.0f : (v > 1.0f ? 1.0f : v);
 }
 
 // Floating-point version of 1D interpolation
--- pdfium.old/third_party/lcms/src/lcms2_internal.h
+++ pdfium/third_party/lcms/src/lcms2_internal.h
@@ -108,7 +108,7 @@
 /// older MSVC versions.
 # if defined(_MSC_VER) && _MSC_VER <= 1700
         #include <float.h>
-        #define isnan _isnan
+        #define std::isnan _std::isnan
         #define isinf(x) (!_finite((x)))
 # endif
 
--- pdfium.old/xfa/fgas/graphics/cfgas_gegraphics.cpp
+++ pdfium/xfa/fgas/graphics/cfgas_gegraphics.cpp
@@ -313,7 +313,7 @@
             float x = static_cast<float>(column);
             scale = (((x - start_x) * x_span) + ((y - start_y) * y_span)) /
                     axis_len_square;
-            if (isnan(scale) || scale < 0.0f) {
+            if (std::isnan(scale) || scale < 0.0f) {
               if (!info_.fillColor.GetShading()->IsExtendedBegin()) {
                 continue;
               }
@@ -374,7 +374,7 @@
               continue;
             }
           }
-          if (isnan(s) || s < 0.0f) {
+          if (std::isnan(s) || s < 0.0f) {
             if (!info_.fillColor.GetShading()->IsExtendedBegin()) {
               continue;
             }
--- pdfium.old/xfa/fxfa/parser/cxfa_measurement.cpp
+++ pdfium/xfa/fxfa/parser/cxfa_measurement.cpp
@@ -46,7 +46,7 @@
 
   size_t nUsedLen = 0;
   float fValue = FXSYS_wcstof(wsMeasure, &nUsedLen);
-  if (!isfinite(fValue)) {
+  if (!std::isfinite(fValue)) {
     fValue = 0.0f;
   }
   Set(fValue, GetUnitFromString(wsMeasure.Substr(nUsedLen)));