pitrou commented on a change in pull request #7945:
URL: https://github.com/apache/arrow/pull/7945#discussion_r471472052
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File path: cpp/src/arrow/util/decimal.cc
##########
@@ -241,64 +284,43 @@ Decimal128::operator int64_t() const {
return static_cast<int64_t>(low_bits());
}
-static std::string ToStringNegativeScale(const std::string& str,
- int32_t adjusted_exponent, bool
is_negative) {
- std::stringstream buf;
-
- size_t offset = 0;
- buf << str[offset++];
-
- if (is_negative) {
- buf << str[offset++];
- }
-
- buf << '.' << str.substr(offset, std::string::npos) << 'E' << std::showpos
- << adjusted_exponent;
- return buf.str();
-}
-
-std::string Decimal128::ToString(int32_t scale) const {
- const std::string str(ToIntegerString());
-
+static void AdjustIntegerStringWithScale(int32_t scale, std::string* str) {
if (scale == 0) {
- return str;
+ return;
}
- const bool is_negative = *this < 0;
-
- const auto len = static_cast<int32_t>(str.size());
+ const bool is_negative = str->front() == '-';
const auto is_negative_offset = static_cast<int32_t>(is_negative);
- const int32_t adjusted_exponent = -scale + (len - 1 - is_negative_offset);
+ const auto len = static_cast<int32_t>(str->size());
+ const int32_t num_digits = len - is_negative_offset;
+ const int32_t adjusted_exponent = num_digits - 1 - scale;
/// Note that the -6 is taken from the Java BigDecimal documentation.
if (scale < 0 || adjusted_exponent < -6) {
- return ToStringNegativeScale(str, adjusted_exponent, is_negative);
+ str->insert(str->begin() + 1 + is_negative_offset, '.');
+ str->push_back('E');
+ // Use stringstream only for printing the exponent integer. It should be
short
+ // enough to avoid memory allocations.
+ std::stringstream buf;
+ buf << std::showpos << adjusted_exponent;
+ *str += buf.str();
+ return;
}
- if (is_negative) {
- if (len - 1 > scale) {
- const auto n = static_cast<size_t>(len - scale);
- return str.substr(0, n) + "." + str.substr(n,
static_cast<size_t>(scale));
- }
-
- if (len - 1 == scale) {
- return "-0." + str.substr(1, std::string::npos);
- }
-
- std::string result("-0." + std::string(static_cast<size_t>(scale - len +
1), '0'));
- return result + str.substr(1, std::string::npos);
- }
-
- if (len > scale) {
+ if (num_digits > scale) {
const auto n = static_cast<size_t>(len - scale);
- return str.substr(0, n) + "." + str.substr(n, static_cast<size_t>(scale));
+ str->insert(str->begin() + n, '.');
+ return;
}
- if (len == scale) {
- return "0." + str;
- }
+ str->insert(is_negative_offset, scale - num_digits + 2, '0');
Review comment:
Thank you!
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