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String conversion perf improvements + minor unrelated changes #54

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String conversion perf improvements + minor unrelated changes #54

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23a8c00
Improve performance of string conversion
louiswins Oct 29, 2019
903c351
Explicitly discard CoCreateGuid HRESULT
louiswins Oct 29, 2019
9b51a5d
Mark a couple functions static
louiswins Oct 29, 2019
1ef5038
Clearer names for locals
louiswins Oct 29, 2019
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35 changes: 12 additions & 23 deletions src/guid.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -113,27 +113,16 @@ bool Guid::isValid() const
// convert to string using std::snprintf() and std::string
std::string Guid::str() const
{
char one[10], two[6], three[6], four[6], five[14];

snprintf(one, 10, "%02x%02x%02x%02x",
_bytes[0], _bytes[1], _bytes[2], _bytes[3]);
snprintf(two, 6, "%02x%02x",
_bytes[4], _bytes[5]);
snprintf(three, 6, "%02x%02x",
_bytes[6], _bytes[7]);
snprintf(four, 6, "%02x%02x",
_bytes[8], _bytes[9]);
snprintf(five, 14, "%02x%02x%02x%02x%02x%02x",
constexpr size_t guidBufferSize = sizeof("01234567-0123-0123-0123-0123456789ab");
char buffer[guidBufferSize];
snprintf(buffer, guidBufferSize, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
_bytes[0], _bytes[1], _bytes[2], _bytes[3],
_bytes[4], _bytes[5],
_bytes[6], _bytes[7],
_bytes[8], _bytes[9],
_bytes[10], _bytes[11], _bytes[12], _bytes[13], _bytes[14], _bytes[15]);
const std::string sep("-");
std::string out(one);

out += sep + two;
out += sep + three;
out += sep + four;
out += sep + five;

return out;
return std::string(buffer, guidBufferSize - 1);
}

// conversion operator for std::string
Expand All @@ -157,7 +146,7 @@ Guid::Guid(std::array<unsigned char, 16> &&bytes) : _bytes(std::move(bytes))
{ }

// converts a single hex char to a number (0 - 15)
unsigned char hexDigitToChar(char ch)
static unsigned char hexDigitToChar(char ch)
{
// 0-9
if (ch > 47 && ch < 58)
Expand All @@ -174,7 +163,7 @@ unsigned char hexDigitToChar(char ch)
return 0;
}

bool isValidHexChar(char ch)
static bool isValidHexChar(char ch)
{
// 0-9
if (ch > 47 && ch < 58)
Expand All @@ -192,7 +181,7 @@ bool isValidHexChar(char ch)
}

// converts the two hexadecimal characters to an unsigned char (a byte)
unsigned char hexPairToChar(char a, char b)
static unsigned char hexPairToChar(char a, char b)
{
return hexDigitToChar(a) * 16 + hexDigitToChar(b);
}
Expand Down Expand Up @@ -315,7 +304,7 @@ Guid newGuid()
Guid newGuid()
{
GUID newId;
CoCreateGuid(&newId);
(void)CoCreateGuid(&newId);

std::array<unsigned char, 16> bytes =
{
Expand Down