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Small improvements on Dragonbox #1887

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Sep 20, 2020
Merged

Small improvements on Dragonbox #1887

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31 changes: 17 additions & 14 deletions include/fmt/format-inl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1870,8 +1870,8 @@ template <> struct float_info<float> {
static const int case_fc_upper_threshold = 6;
static const int case_shorter_interval_left_endpoint_lower_threshold = 2;
static const int case_shorter_interval_left_endpoint_upper_threshold = 3;
static const int shorter_interval_case_tie_lower_threshold = -35;
static const int shorter_interval_case_tie_upper_threshold = -35;
static const int shorter_interval_tie_lower_threshold = -35;
static const int shorter_interval_tie_upper_threshold = -35;
static const int max_trailing_zeros = 7;
};

Expand All @@ -1896,8 +1896,8 @@ template <> struct float_info<double> {
static const int case_fc_upper_threshold = 9;
static const int case_shorter_interval_left_endpoint_lower_threshold = 2;
static const int case_shorter_interval_left_endpoint_upper_threshold = 3;
static const int shorter_interval_case_tie_lower_threshold = -77;
static const int shorter_interval_case_tie_upper_threshold = -77;
static const int shorter_interval_tie_lower_threshold = -77;
static const int shorter_interval_tie_upper_threshold = -77;
static const int max_trailing_zeros = 16;
};

Expand Down Expand Up @@ -2061,9 +2061,10 @@ template <> struct cache_accessor<float> {

static carrier_uint compute_round_up_for_shorter_interval_case(
const cache_entry_type& cache, int beta_minus_1) FMT_NOEXCEPT {
return carrier_uint(((cache >> (64 - float_info<float>::significand_bits -
2 - beta_minus_1)) +
1)) /
return (static_cast<carrier_uint>(
cache >>
(64 - float_info<float>::significand_bits - 2 - beta_minus_1)) +
1) /
2;
}
};
Expand Down Expand Up @@ -2377,8 +2378,8 @@ FMT_ALWAYS_INLINE FMT_SAFEBUFFERS void shorter_interval_case(
ret_value.exponent = minus_k;

// When tie occurs, choose one of them according to the rule
if (exponent >= float_info<T>::shorter_interval_case_tie_lower_threshold &&
exponent <= float_info<T>::shorter_interval_case_tie_upper_threshold) {
if (exponent >= float_info<T>::shorter_interval_tie_lower_threshold &&
exponent <= float_info<T>::shorter_interval_tie_upper_threshold) {
ret_value.significand = ret_value.significand % 2 == 0
? ret_value.significand
: ret_value.significand - 1;
Expand Down Expand Up @@ -2411,7 +2412,7 @@ template <class T> FMT_SAFEBUFFERS decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT {
if (exponent != 0) {
exponent += float_info<T>::exponent_bias - float_info<T>::significand_bits;

// Closer boundary case; proceed like Schubfach
// Shorter interval case; proceed like Schubfach
if (significand == 0) {
shorter_interval_case<T>(ret_value, exponent);
return ret_value;
Expand Down Expand Up @@ -2461,10 +2462,12 @@ template <class T> FMT_SAFEBUFFERS decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT {
}
} else {
// r == deltai; compare fractional parts
// Check conditions in the order different from the paper
// to take advantage of short-circuiting
const carrier_uint two_fl = two_fc - 1;
if (!cache_accessor<T>::compute_mul_parity(two_fl, cache, beta_minus_1) &&
(!include_left_endpoint ||
!is_endpoint_integer<T>(two_fl, exponent, minus_k))) {
if ((!include_left_endpoint ||
!is_endpoint_integer<T>(two_fl, exponent, minus_k)) &&
!cache_accessor<T>::compute_mul_parity(two_fl, cache, beta_minus_1)) {
goto small_divisor_case_label;
}
}
Expand Down Expand Up @@ -2497,7 +2500,7 @@ template <class T> FMT_SAFEBUFFERS decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT {
// We have either yi == zi - epsiloni or yi == (zi - epsiloni) - 1,
// where yi == zi - epsiloni if and only if z^(f) >= epsilon^(f)
// Since there are only 2 possibilities, we only need to care about the
// parity Also, zi and r should have the same parity since the divisor
// parity. Also, zi and r should have the same parity since the divisor
// is an even number
if (cache_accessor<T>::compute_mul_parity(two_fc, cache, beta_minus_1) !=
approx_y_parity) {
Expand Down