diff --git a/stint/intops.nim b/stint/intops.nim index 5c52322..8a8ae76 100644 --- a/stint/intops.nim +++ b/stint/intops.nim @@ -184,12 +184,12 @@ func setBit*(a: var StInt, k: Natural) = func clearBit*(a: var StInt, k: Natural) = ## set bit at position `k` - ## k = 0..a.bits-1 + ## k = 0..a.bits-1 a.imp.clearBit(k) func getBit*(a: StInt, k: Natural): bool = ## set bit at position `k` - ## k = 0..a.bits-1 + ## k = 0..a.bits-1 a.imp.getBit(k) {.pop.} @@ -234,10 +234,29 @@ func `+=`*(a: var StInt, b: SomeUnsignedInt) = {.push raises: [], noinit, gcsafe.} -func pow*(a: StUint, e: Natural): StUint = +func isOdd(x: Natural): bool = + bool(x and 1) + +func pow*(a: StInt, e: Natural): StInt = ## Compute ``a`` to the power of ``e``, ## ``e`` must be non-negative - -func pow*[aBits, eBits](a: StUint[aBits], e: StUint[eBits]): StUint[aBits] = + if a.isNegative: + let base = a.neg + result.imp = base.imp.pow(e) + if e.isOdd: + result.negate + else: + result.imp = a.imp.pow(e) + +func pow*[aBits, eBits](a: StInt[aBits], e: StInt[eBits]): StInt[aBits] = ## Compute ``x`` to the power of ``y``, - ## ``x`` must be non-negative \ No newline at end of file + ## ``x`` must be non-negative + doAssert e.isNegative.not, "exponent must be non-negative" + + if a.isNegative: + let base = a.neg + result.imp = base.imp.pow(e.imp) + if e.isOdd: + result.negate + else: + result.imp = a.imp.pow(e.imp) diff --git a/tests/test_int_addsub.nim b/tests/test_int_addsub.nim index cd99636..b1c51e2 100644 --- a/tests/test_int_addsub.nim +++ b/tests/test_int_addsub.nim @@ -92,10 +92,10 @@ template testAddSub(chk, tst: untyped) = chkNegation(chk, 32767, -32767, 128) # With Nim 1.6, it seems like https://github.com/status-im/nim-stint/issues/92 # can now happen on 32-bit platforms. - when (NimMajor,NimMinor,NimPatch) < (1,6,0): - chkNegation(chk, 2147483648, -2147483648, 128) + #when (NimMajor,NimMinor,NimPatch) < (1,6,0): + chkNegation(chk, 2147483648, -2147483648, 128) chkNegation(chk, 2147483647, -2147483647, 128) - #chkNegation(chk, 9223372036854775808, -9223372036854775808, 128) # TODO: bug #92 + # chkNegation(chk, 9223372036854775808, -9223372036854775808, 128) # TODO: bug #92 tst "absolute integer": chkAbs(chk, 0, 0, 128) diff --git a/tests/test_int_exp.nim b/tests/test_int_exp.nim new file mode 100644 index 0000000..24bf4eb --- /dev/null +++ b/tests/test_int_exp.nim @@ -0,0 +1,64 @@ +# Stint +# Copyright 2018-2023 Status Research & Development GmbH +# Licensed under either of +# +# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0) +# * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT) +# +# at your option. This file may not be copied, modified, or distributed except according to those terms. + +import ../stint, unittest, math, test_helpers + +template chkPow(chk: untyped, a, b, c: string, bits: int) = + chk pow(fromHex(StInt[bits], a), fromHex(StInt[bits], b)) == fromHex(StInt[bits], c) + +template chkPow(chk: untyped, a: string, b: SomeInteger, c: string, bits: int) = + chk pow(fromHex(StInt[bits], a), b) == fromHex(StInt[bits], c) + +template testExp(chk, tst: untyped) = + tst "signed BigInt BigInt Pow": + chkPow(chk, "F", "2", "E1", 128) + chkPow(chk, "FF", "2", "FE01", 128) + chkPow(chk, "FF", "3", "FD02FF", 128) + chkPow(chk, "FFF", "3", "FFD002FFF", 128) + chkPow(chk, "FFFFF", "3", "ffffd00002fffff", 128) + + chk pow(-10.i128, 2.i128) == 100.i128 + chk pow(-10.i128, 3.i128) == -1000.i128 + + tst "signed BigInt Natural Pow": + chkPow(chk, "F", 2, "E1", 128) + chkPow(chk, "FF", 2, "FE01", 128) + chkPow(chk, "FF", 3, "FD02FF", 128) + chkPow(chk, "FFF", 3, "FFD002FFF", 128) + chkPow(chk, "FFFFF", 3, "ffffd00002fffff", 128) + + chk pow(-10.i128, 2) == 100.i128 + chk pow(-10.i128, 3) == -1000.i128 + +static: + testExp(ctCheck, ctTest) + +suite "Wider signed int exp coverage": + testExp(check, test) + +suite "Testing signed exponentiation": + test "Simple exponentiation 5^3": + + let + a = 5'u64 + b = 3 + u = a.stint(64) + + check: + cast[uint64](u.pow(b)) == a ^ b + cast[uint64](u.pow(b.stint(64))) == a ^ b + + test "12 ^ 34 == 4922235242952026704037113243122008064": + # https://www.wolframalpha.com/input/?i=12+%5E+34 + let + a = 12.stint(256) + b = 34 + + check: a.pow(b) == "4922235242952026704037113243122008064".i256 + check: a.pow(b.stint(256)) == "4922235242952026704037113243122008064".i256