[core] add the ability to stringy numbers as hex

include/mbgl/util/string.hpp

@@ -53,6 +53,8 @@ std::string toString(float, bool decimal = false);
 std::string toString(double, bool decimal = false);
 std::string toString(long double, bool decimal = false);
 
+std::string toHex(size_t);
+
 inline std::string toString(std::exception_ptr error) {
     assert(error);
 

src/mbgl/util/string.cpp

@@ -15,6 +15,25 @@ std::string toString(double num, bool decimal) {
 std::string toString(long double num, bool decimal) {
     return dtoa(num, decimal);
 }
+
+namespace {
+
+template <typename T>
+std::string toPaddedHex(T x) {
+    std::string result;
+    result.resize(sizeof(T) * 2);
+    for (int index = sizeof(T) * 2 - 1; index >= 0; index--) {
+        const int digit = x & 0x0F;
+        result[index] = '0' + digit + (digit > 9 ? 39 : 0);
+        x >>= 4;
+    }
+    return result;
+}
+
+}
+
+std::string toHex(size_t value) {
+    return toPaddedHex(value);
 }
 
 } // namespace util

test/util/string.test.cpp

@@ -2,6 +2,8 @@
 
 #include <mbgl/util/string.hpp>
 
+#include <cstdint>
+
 using namespace mbgl;
 
 TEST(ToString, FloatingPoint) {
@@ -16,3 +18,12 @@ TEST(ToString, FloatingPoint) {
     EXPECT_EQ("12340000000", util::toString(12340000000.0));
     EXPECT_EQ("12340000000.0", util::toString(12340000000.0, true));
 }
+
+TEST(ToHex, SIZE_T) {
+#if INTPTR_MAX == INT32_MAX
+    EXPECT_EQ("a715b247", util::toHex((size_t)0xa715b247));
+#elif INTPTR_MAX == INT64_MAX
+    EXPECT_EQ("a715b247df38cc29", util::toHex((size_t)0xa715b247df38cc29));
+#endif
+
+}