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Add setBit, clearBit and testBit #107

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Add setBit, clearBit and testBit #107

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536d6c0
Add setBit, clearBit and testBit
demotomohiro Jul 10, 2022
31d0447
Fix errors on nim-1.4.8
demotomohiro Jul 12, 2022
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46 changes: 46 additions & 0 deletions src/bigints.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -1198,3 +1198,49 @@ func powmod*(base, exponent, modulus: BigInt): BigInt =
result = (result * basePow) mod modulus
basePow = (basePow * basePow) mod modulus
exponent = exponent shr 1

func getLimbAndBitPosFromBitPos(bit: Natural): tuple[bit, limb: Natural] {.inline.} =
(bit: Natural(bit and 31), limb: Natural(bit shr 5))

func setBit*(a: var BigInt; bit: Natural) =
## Mutates `a`, with the bit at position `bit` set to 1.
runnableExamples:
var v = 0b0000_0011.initBigInt
v.setBit(5)
doAssert v == 0b0010_0011.initBigInt

let (b, l) = getLimbAndBitPosFromBitPos(bit)

if l >= a.limbs.len:
a.limbs.setLen(l + 1)

a.limbs[l] = a.limbs[l] or (1'u32 shl b)

func clearBit*(a: var BigInt; bit: Natural) =
## Mutates `v`, with the bit at position `bit` set to 0.
runnableExamples:
var v = 0b0000_0011.initBigInt
v.clearBit(1)
doAssert v == 0b0000_0001.initBigInt

let (b, l) = getLimbAndBitPosFromBitPos(bit)

if l >= a.limbs.len:
return

a.limbs[l] = a.limbs[l] and not (1'u32 shl b)
normalize(a)

func testBit*(a: BigInt; bit: Natural): bool =
## Returns true if the bit in `a` at positions `bit` is set to 1.
runnableExamples:
let v = 0b0000_1111.initBigInt
doAssert v.testBit(0)
doAssert not v.testBit(7)

let (b, l) = getLimbAndBitPosFromBitPos(bit)

if l >= a.limbs.len:
false
else:
(a.limbs[l] and (1'u32 shl b)) != 0
82 changes: 82 additions & 0 deletions tests/tbigints.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -786,6 +786,88 @@ proc main() =
doAssert pred(a, 3) == initBigInt(4)
doAssert succ(a, 3) == initBigInt(10)

block: # setBit/clearBit/clearBit
var a = initBigInt(0)
for i in 0..256:
doAssert not a.testBit(i)
for i in 0..256:
a.setBit(i)
for j in 0..i:
doAssert a.testBit(j)
for j in (i + 1)..256:
doAssert not a.testBit(j)
for i in countDown(256, 0):
doAssert a.testBit(i)
for i in countDown(256, 0):
a.clearBit(i)
for j in 0..(i - 1):
doAssert a.testBit(j)
for j in i..256:
doAssert not a.testBit(j)
for i in countDown(256, 0):
doAssert not a.testBit(i)
for i in 1..256:
a.setBit(i)
doAssert a.testBit(i)
doAssert not a.testBit(i - 1)
doAssert not a.testBit(i + 1)
a.clearBit(i)
doAssert not a.testBit(i)
doAssert not a.testBit(i - 1)
doAssert not a.testBit(i + 1)
doAssert a == initBigInt(0)

a = initBigInt(0)
a.setBit(0)
doAssert a == initBigInt(1)
doAssert a.testBit(0)
a.setBit(1)
doAssert a == initBigInt(3)
doAssert a.testBit(0) and a.testBit(1)
a.setBit(31)
doAssert a == initBigInt((1 shl 31) + 3)
doAssert a.testBit(0) and a.testBit(1) and a.testBit(31)
a.setBit(30)
doAssert a == initBigInt((1 shl 31) + (1 shl 30) + 3)
doAssert a.testBit(0) and a.testBit(1) and a.testBit(30) and a.testBit(31)
a.clearBit(31)
doAssert a == initBigInt((1 shl 30) + 3)
doAssert a.testBit(0) and a.testBit(1) and a.testBit(30) and (not a.testBit(31))
a.clearBit(30)
doAssert a == initBigInt(3)
doAssert a.testBit(0) and a.testBit(1) and (not a.testBit(30)) and (not a.testBit(31))
a.clearBit(1)
doAssert a == initBigInt(1)
doAssert a.testBit(0) and (not a.testBit(1)) and (not a.testBit(30)) and (not a.testBit(31))
a.clearBit(0)
doAssert a == initBigInt(0)

a = initBigInt(0)
a.setBit(63)
doAssert a == initBigInt(1'u64 shl 63'u64)
doAssert (not a.testBit(1)) and (not a.testBit(31)) and (not a.testBit(32)) and a.testBit(63)
a.setBit(1)
doAssert a == initBigInt((1'u64 shl 63'u64) + 2)
doAssert a.testBit(1) and (not a.testBit(31)) and (not a.testBit(32)) and a.testBit(63)
a.setBit(32)
doAssert a == initBigInt((1'u64 shl 63'u64) + (1'u64 shl 32'u64) + 2)
doAssert a.testBit(1) and (not a.testBit(31)) and a.testBit(32) and a.testBit(63)
a.setBit(31)
doAssert a == initBigInt((1'u64 shl 63'u64) + (1'u64 shl 32'u64) + (1'u64 shl 31'u64) + 2)
doAssert a.testBit(1) and a.testBit(31) and a.testBit(32) and a.testBit(63)

a.clearBit(63)
doAssert a == initBigInt((1'u64 shl 32'u64) + (1'u64 shl 31'u64) + 2)
doAssert a.testBit(1) and a.testBit(31) and a.testBit(32) and (not a.testBit(63))
a.clearBit(1)
doAssert a == initBigInt((1'u64 shl 32'u64) + (1'u64 shl 31'u64))
doAssert (not a.testBit(1)) and a.testBit(31) and a.testBit(32) and (not a.testBit(63))
a.clearBit(32)
doAssert a == initBigInt((1'u64 shl 31'u64))
doAssert (not a.testBit(1)) and a.testBit(31) and (not a.testBit(32)) and (not a.testBit(63))
a.clearBit(31)
doAssert a == initBigInt(0)
doAssert (not a.testBit(1)) and (not a.testBit(31)) and (not a.testBit(32)) and (not a.testBit(63))

static: main()
main()