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module decimal | |
record Decimal : Nat -> Type where | |
MkDecimal : (places : Nat) -> (mantissa : Integer) -> Decimal places | |
signum : Integer -> Integer | |
signum n = case compare n 0 of | |
LT => (-1) | |
EQ => 0 | |
GT => 1 | |
divRound : Integer -> Integer -> Integer | |
divRound n1 n2 = if (abs r * 2) >= (abs n2) then n + (signum n1) else n where | |
n = n1 `div` n2 | |
r = n1 `mod` n2 | |
power' : Integer -> Nat -> Integer | |
power' x Z = 1 | |
power' x n = x * (x `power'` (n-1)) | |
roundTo : (np : Nat) -> Decimal op-> Decimal np | |
roundTo np d = case d of | |
MkDecimal op m => MkDecimal np (calc m) | |
where | |
divisor : Integer | |
divisor = 10 `power'` (op-np) | |
multiplier : Integer | |
multiplier = 10 `power'` (np-op) | |
calc : Integer -> Integer | |
calc m = case compare np op of | |
LT => m `divRound` divisor | |
EQ => m | |
GT => m * multiplier |
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*decimal> :let d : Decimal 3; d = MkDecimal 3 123456 | |
*decimal> d | |
MkDecimal 3 123456 : Decimal 3 | |
*decimal> mantissa d | |
123456 : Integer | |
*decimal> roundTo 2 d | |
MkDecimal 2 12346 : Decimal 2 | |
*decimal> roundTo 5 d | |
MkDecimal 5 12345600 : Decimal 5 |
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