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lib/decimal: optimize maxUpExponent() by eliminating division from hot path

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This commit is contained in:
Aliaksandr Valialkin 2020-09-19 13:49:16 +03:00
parent df547bf345
commit 604e8f6114
1 changed files with 20 additions and 22 deletions
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42
lib/decimal/decimal.go
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@ -239,6 +239,8 @@ type vaeBuf struct {
var vaeBufPool sync.Pool
const int64Max = int64(1<<63 - 1)
func maxUpExponent(v int64) int16 {
if v == 0 {
// Any exponent allowed.
@ -251,46 +253,42 @@ func maxUpExponent(v int64) int16 {
// Handle corner case for v=-1<<63
return 0
}
maxMultiplier := ((1 << 63) - 1) / uint64(v)
switch {
case maxMultiplier >= 1e19:
return 19
case maxMultiplier >= 1e18:
case v <= int64Max/1e18:
return 18
case maxMultiplier >= 1e17:
case v <= int64Max/1e17:
return 17
case maxMultiplier >= 1e16:
case v <= int64Max/1e16:
return 16
case maxMultiplier >= 1e15:
case v <= int64Max/1e15:
return 15
case maxMultiplier >= 1e14:
case v <= int64Max/1e14:
return 14
case maxMultiplier >= 1e13:
case v <= int64Max/1e13:
return 13
case maxMultiplier >= 1e12:
case v <= int64Max/1e12:
return 12
case maxMultiplier >= 1e11:
case v <= int64Max/1e11:
return 11
case maxMultiplier >= 1e10:
case v <= int64Max/1e10:
return 10
case maxMultiplier >= 1e9:
case v <= int64Max/1e9:
return 9
case maxMultiplier >= 1e8:
case v <= int64Max/1e8:
return 8
case maxMultiplier >= 1e7:
case v <= int64Max/1e7:
return 7
case maxMultiplier >= 1e6:
case v <= int64Max/1e6:
return 6
case maxMultiplier >= 1e5:
case v <= int64Max/1e5:
return 5
case maxMultiplier >= 1e4:
case v <= int64Max/1e4:
return 4
case maxMultiplier >= 1e3:
case v <= int64Max/1e3:
return 3
case maxMultiplier >= 1e2:
case v <= int64Max/1e2:
return 2
case maxMultiplier >= 1e1:
case v <= int64Max/1e1:
return 1
default:
return 0