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Set the write part to use simpler math with u128

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Julius de Bruijn 2020-07-04 13:31:45 +02:00 committed by Austin Bonander
parent f246d41aed
commit e45e6d4173
1 changed files with 18 additions and 59 deletions
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77
sqlx-core/src/postgres/types/decimal.rs
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@ -107,34 +107,35 @@ impl TryFrom<&'_ Decimal> for PgNumeric {
// Bytes 13-16: high portion of m // Bytes 13-16: high portion of m
let s = decimal.serialize(); let s = decimal.serialize();
// As u96. // Moving the flags from the beginning of the array to the end, giving
let mut mantissa = [ // us a representation of u96 we can convert to u128.
// lo //
u32::from_le_bytes(s[4..8].try_into().unwrap()), // We also just set the flags as zero, so we don't need to chop them off
// mid // from the resulting integer.
u32::from_le_bytes(s[8..12].try_into().unwrap()), let mut mantissa = u128::from_le_bytes([
// hi s[4], s[5], s[6], s[7], // lo portion
u32::from_le_bytes(s[12..16].try_into().unwrap()), s[8], s[9], s[10], s[11], // mid portion
// flags s[12], s[13], s[14], s[15], // hi portion
0u32, 0, 0, 0, 0, // flags (cleared)
]; ]);
// If our scale is not a multiple of 4, we need to go to the next // If our scale is not a multiple of 4, we need to go to the next
// multiple. // multiple.
let groups_diff = scale % 4; let groups_diff = scale % 4;
if groups_diff > 0 { if groups_diff > 0 {
let remainder: u16 = 4 - groups_diff; let remainder = 4 - groups_diff as u32;
let power = 10u32.pow(remainder as u32); let power = 10u32.pow(remainder as u32) as u128;
mul_by_u32(&mut mantissa, power);
mantissa = mantissa * power;
} }
// Array to store max mantissa of Decimal in Postgres decimal format. // Array to store max mantissa of Decimal in Postgres decimal format.
let mut digits = Vec::with_capacity(8); let mut digits = Vec::with_capacity(8);
// Convert to base-10000. // Convert to base-10000.
while !mantissa.iter().all(|b| *b == 0) { while mantissa != 0 {
let remainder = div_by_u32(&mut mantissa, 10000) as u16; digits.push((mantissa % 10_000) as i16);
digits.push(remainder as i16) mantissa /= 10_000;
} }
// Change the endianness. // Change the endianness.
@ -182,48 +183,6 @@ impl Decode<'_, Postgres> for Decimal {
} }
} }
// Returns remainder
fn div_by_u32(bits: &mut [u32], divisor: u32) -> u32 {
assert_ne!(0, divisor);
if divisor == 1 {
// dividend remains unchanged
0
} else {
let mut remainder = 0u32;
let divisor = u64::from(divisor);
for part in bits.iter_mut().rev() {
let temp = (u64::from(remainder) << 32) + u64::from(*part);
remainder = (temp % divisor) as u32;
*part = (temp / divisor) as u32;
}
remainder
}
}
fn mul_by_u32(bits: &mut [u32], m: u32) -> u32 {
let mut overflow = 0;
for num in bits.iter_mut() {
let (lo, hi) = mul_part(*num, m, overflow);
*num = lo;
overflow = hi;
}
overflow
}
fn mul_part(left: u32, right: u32, high: u32) -> (u32, u32) {
let result = u64::from(left) * u64::from(right) + u64::from(high);
let hi = (result >> 32) as u32;
let lo = result as u32;
(lo, hi)
}
#[cfg(test)] #[cfg(test)]
mod decimal_to_pgnumeric { mod decimal_to_pgnumeric {
use super::{Decimal, PgNumeric, PgNumericSign}; use super::{Decimal, PgNumeric, PgNumericSign};