String32.hh

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#ifndef STRING32_HH
#define STRING32_HH
 
#include "narrow.hh"
#include <cassert>
#include <cstdint>
#include <type_traits>
 
// Given a buffer of max size 4GB, 32 bits are enough to address each position
// in that buffer.
// - On 32-bit systems we can use a pointer to a location in the buffer.
// - On 64-bit systems a pointer is too large (64 bit), but an index in the
//   buffer works fine. (An index works fine on 32-bit systems as well, but is
//   slightly less efficient).
// The String32 helper abstracts the difference between the two above
// approaches. In both cases it is a 32-bit type (hence the name). And on
// both 32/64-bit systems it uses the more efficient implementation.
 
using String32 = std::conditional_t<
        (sizeof(char*) > sizeof(uint32_t)), // is a pointer bigger than an uint32_t
        uint32_t,                           // yes -> use uint32_t
        const char*>;                       // no  -> directly use pointer
 
// convert string in buffer to String32
constexpr void toString32(const char* buffer, const char* str, uint32_t& result) {
        assert(buffer <= str);
        result = narrow<uint32_t>(str - buffer);
}
constexpr void toString32(const char* /*buffer*/, const char* str, const char*& result) {
        result = str;
}
 
// convert String32 back to string in buffer
[[nodiscard]] constexpr const char* fromString32(const char* buffer, uint32_t str32) {
        return buffer + str32;
}
[[nodiscard]] constexpr const char* fromString32(const char* /*buffer*/, const char* str32) {
        return str32;
}
 
#endif