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atod optim and cleanup #15

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Merged
mrabine merged 1 commit into from
Dec 4, 2025
Merged

atod optim and cleanup #15

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59 changes: 33 additions & 26 deletions dconv/include/dconv/atod.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -63,11 +63,11 @@ namespace dconv
return end;
}

inline void umul192 (uint64_t hi, uint64_t lo, uint64_t mantissa, uint64_t& high, uint64_t& middle, uint64_t& low) noexcept
inline void umul192 (uint64_t hi, uint64_t lo, uint64_t significand, uint64_t& high, uint64_t& middle, uint64_t& low) noexcept
{
#if defined(__SIZEOF_INT128__)
__uint128_t h = static_cast <__uint128_t> (hi) * mantissa;
__uint128_t l = static_cast <__uint128_t> (lo) * mantissa;
__uint128_t h = static_cast <__uint128_t> (hi) * significand;
__uint128_t l = static_cast <__uint128_t> (lo) * significand;
__uint128_t s = h + (l >> 64);

high = static_cast <uint64_t> (s >> 64);
Expand All @@ -76,8 +76,8 @@ namespace dconv
#else
uint64_t hi_hi, hi_lo, lo_hi, lo_lo;

uint64_t m_lo = static_cast <uint32_t> (mantissa);
uint64_t m_hi = mantissa >> 32;
uint64_t m_lo = static_cast <uint32_t> (significand);
uint64_t m_hi = significand >> 32;
uint64_t p0 = (hi & 0xFFFFFFFF) * m_lo;
uint64_t p1 = (hi >> 32) * m_lo;
uint64_t p2 = (hi & 0xFFFFFFFF) * m_hi;
Expand All @@ -100,36 +100,43 @@ namespace dconv
#endif
}

inline bool strtodFast (bool negative, uint64_t mantissa, int64_t exponent, double& value) noexcept
inline bool strtodFast (bool negative, uint64_t significand, int64_t exponent, double& value) noexcept
{
static constexpr double pow10[] = {
1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10,
1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21,
1e22
};

if (unlikely (mantissa == 0))
value = static_cast <double> (significand);

if (unlikely((exponent > 22) && (exponent < (22 + 16))))
{
value = negative ? -0.0 : 0.0;
return true;
value *= pow10[exponent - 22];
exponent = 22;
}

if (likely ((exponent >= -22) && (exponent <= 22) && (mantissa <= 9007199254740991)))
if (likely ((exponent >= -22) && (exponent <= 22) && (value <= 9007199254740991.0)))
{
value = static_cast <double> (mantissa);
value = (exponent < 0) ? (value / pow10[-exponent]) : (value * pow10[exponent]);
value = negative ? -value : value;
return true;
}

if (unlikely (value == 0.0))
{
value = negative ? -0.0 : 0.0;
return true;
}

if (unlikely (exponent < -325 || exponent > 308))
{
return false;
}

uint64_t high, middle, low;
const Power& power = atodpow[exponent + 325];
umul192 (power.hi, power.lo, mantissa, high, middle, low);
umul192 (power.hi, power.lo, significand, high, middle, low);
int64_t exp = ((exponent * 217706) >> 16) + 1087;

int lz;
Expand Down Expand Up @@ -181,12 +188,12 @@ namespace dconv
return true;
}

constexpr inline bool isDigit (char c) noexcept
inline constexpr bool isDigit (char c) noexcept
{
return static_cast <unsigned char> (c - '0') <= 9u;
}

constexpr inline bool isSign (char c) noexcept
inline constexpr bool isSign (char c) noexcept
{
return (c == '+') || (c == '-');
}
Expand All @@ -195,7 +202,7 @@ namespace dconv
{
auto beg = view.data ();

uint64_t mantissa = 0;
uint64_t significand = 0;
uint64_t digits = 0;
bool neg = view.getIf ('-');

Expand All @@ -208,17 +215,17 @@ namespace dconv
}
else if (likely (isDigit (view.peek ())))
{
mantissa = view.get () - '0';
significand = view.get () - '0';
++digits;

while (isDigit (view.peek ()))
{
uint64_t next = (10 * mantissa) + (view.get () - '0');
if (unlikely (next < mantissa)) // overflow
uint64_t next = (10 * significand) + (view.get () - '0');
if (unlikely (next < significand)) // overflow
{
return strtodSlow (beg, value);
}
mantissa = next;
significand = next;
++digits;
}
}
Expand Down Expand Up @@ -254,19 +261,19 @@ namespace dconv
return nullptr;
}

mantissa = (10 * mantissa) + (view.get () - '0');
if (mantissa || digits) ++digits;
significand = (10 * significand) + (view.get () - '0');
if (significand || digits) ++digits;
--exponent;

while (isDigit (view.peek ()))
{
uint64_t next = (10 * mantissa) + (view.get () - '0');
if (unlikely (next < mantissa)) // overflow
uint64_t next = (10 * significand) + (view.get () - '0');
if (unlikely (next < significand)) // overflow
{
return strtodSlow (beg, value);
}
mantissa = next;
if (mantissa || digits) ++digits;
significand = next;
if (significand || digits) ++digits;
--exponent;
}
}
Expand Down Expand Up @@ -304,7 +311,7 @@ namespace dconv

if (likely (digits <= 19))
{
if (strtodFast (neg, mantissa, exponent, value))
if (strtodFast (neg, significand, exponent, value))
{
return view.data ();
}
Expand Down
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