28 lines
1.0 KiB
Nim
28 lines
1.0 KiB
Nim
# Mpint
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# Copyright 2018 Status Research & Development GmbH
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# Licensed under either of
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#
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# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
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# * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
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#
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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import ./uint_type, bitops
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proc bit_length*(x: SomeInteger): int {.inline, noSideEffect.}=
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if x == 0: 0
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else: fastlog2(x)
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proc bit_length*(n: MpUintImpl): int {.noSideEffect.}=
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## Calculates how many bits are necessary to represent the number
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const maxHalfRepr = n.lo.type.sizeof * 8 - 1
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# Changing the following to an if expression somehow transform the whole ASM to 5 branches
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# instead of the 4 expected (with the inline ASM from bit_length_impl)
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# Also there does not seems to be a way to generate a conditional mov
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if n.hi.bit_length == 0:
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n.lo.bit_length
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else:
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n.hi.bit_length + maxHalfRepr
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