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Implement floating point conversion #110

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Implement floating point conversion #110

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b38ff2b
Implement toBiggestFloat
rotu Jul 26, 2022
6c73172
don't use BiggestInt in implementation of toBiggestFloat
rotu Jul 27, 2022
b08bbbe
Add tests for infinity
rotu Jul 27, 2022
7fe47ad
support for other floating point types
rotu Jul 28, 2022
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8 changes: 7 additions & 1 deletion src/bigints.nim
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
## Arbitrary precision integers.

import std/[algorithm, bitops, math, options]
import std/[algorithm, bitops, fenv, math, options]

type
BigInt* = object
Expand Down Expand Up @@ -1140,6 +1140,12 @@ func fastLog2*(a: BigInt): int =
return -1
bitops.fastLog2(a.limbs[^1]) + 32*(a.limbs.high)

func to*(x: BigInt, T:type SomeFloat): T =
let lolimb = max(x.limbs.low, x.limbs.high - 1 - mantissaDigits(T) div 32)
for i in lolimb..x.limbs.high:
result += T(x.limbs[i].int64) * pow(2.0, 32.0 * T(i))
if x.isNegative:
result = -result

func invmod*(a, modulus: BigInt): BigInt =
## Compute the modular inverse of `a` modulo `modulus`.
Expand Down
29 changes: 29 additions & 0 deletions tests/tbigints.nim
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Expand Up @@ -786,6 +786,35 @@ proc main() =
doAssert pred(a, 3) == initBigInt(4)
doAssert succ(a, 3) == initBigInt(10)

block: # to float
doAssert initBigInt("1").to(float32) is float32
doAssert initBigInt("1").to(float64) is float64
doAssert initBigInt("1").to(BiggestFloat) is BiggestFloat
doAssert initBigInt("1").to(float) is float

doAssert initBigInt("0").to(BiggestFloat) == 0.0
doAssert initBigInt("1").to(BiggestFloat) == 1.0
doAssert initBigInt("1").to(float32) == 1.0
doAssert initBigInt("1").to(float64) == 1.0

doAssert initBigInt("-1").to(BiggestFloat) == -1.0
doAssert initBigInt(BiggestInt.high).to(BiggestFloat) == BiggestFloat(BiggestInt.high)
doAssert initBigInt(BiggestInt.low).to(BiggestFloat) == BiggestFloat(BiggestInt.low)
doAssert (initBigInt(BiggestInt.high) * initBigInt(4)).to(BiggestFloat) == BiggestFloat(BiggestInt.high) * 4.0
doAssert (initBigInt(BiggestInt.low) * initBigInt(4)).to(BiggestFloat) == BiggestFloat(BiggestInt.low) * 4.0
doAssert (initBigInt("17976931348623157") * initBigInt(10).pow(292)).to(BiggestFloat) == 17976931348623157e292

# limits of exact representability
doAssert initBigInt(1 shl 24).to(float32) == float32(1 shl 24)
doAssert initBigInt(-1 shl 24).to(float32) == float32(-1 shl 24)
doAssert initBigInt(1 shl 53).to(float64) == float64(1 shl 53)
doAssert initBigInt(-1 shl 53).to(float64) == float64(-1 shl 53)
# out of exact integer representation range
doAssert initBigInt(int32.high).to(float32) == float32(int32.high)
doAssert initBigInt(int64.high).to(float64) == float64(int64.high)
# well out out of finite range
doAssert initBigInt("-10").pow(400).to(float64) == Inf
doAssert initBigInt("-10").pow(401).to(float64) == -Inf

static: main()
main()