Fix Format_F to apply culture-specific replacements to floating-point types

src/CLR/CorLib/corlib_native_System_Number.cpp

@@ -705,6 +705,28 @@ int Library_corlib_native_System_Number::Format_F(
 
     bool isIntegerDataType = IsIntegerDataType(dataType);
 
+    // For floating-point types with precision 0, check if we have negative zero case
+    // This happens when a small negative value (e.g., -0.099) rounds to 0
+    bool isNegativeZeroCase = false;
+    if (!isIntegerDataType && precision == 0)
+    {
+        double val = 0.0;
+        if (dataType == DATATYPE_R4)
+        {
+            val = (double)value->NumericByRef().r4;
+        }
+        else if (dataType == DATATYPE_R8)
+        {
+            val = (double)value->NumericByRef().r8;
+        }
+
+        // Check if value is negative and would round to 0 with precision 0
+        if (val < 0.0 && val > -0.5)
+        {
+            isNegativeZeroCase = true;
+        }
+    }
+
     char formatStr[FORMAT_FMTSTR_BUFFER_SIZE];
     snprintf(
         formatStr,
@@ -756,6 +778,28 @@ int Library_corlib_native_System_Number::Format_F(
         ret = ReplaceNegativeSign(buffer, ret, negativeSign);
         ret = ReplaceDecimalSeparator(buffer, ret, decimalSeparator);
     }
+    else if (isIntegerDataType && ret == 0)
+    {
+        // special case: when precision is 0 and value is 0, snprintf returns empty string
+        // we need to output "0" instead
+        buffer[0] = '0';
+        buffer[1] = 0;
+        ret = 1;
+    }
+    // apply culture-specific replacements for floating-point types
+    else if (!isIntegerDataType && ret > 0)
+    {
+        // handle negative zero: if the value was negative but rounds to 0, remove the minus sign
+        if (isNegativeZeroCase && buffer[0] == '-')
+        {
+            // remove the negative sign
+            memmove(buffer, &buffer[1], ret);
+            ret--;
+        }
+
+        ret = ReplaceNegativeSign(buffer, ret, negativeSign);
+        ret = ReplaceDecimalSeparator(buffer, ret, decimalSeparator);
+    }
 
     return ret;
 }