27 lines
1.0 KiB
Nim
27 lines
1.0 KiB
Nim
# Stint
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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 ./datatypes, ./conversion, stdlib_bitops
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export stdlib_bitops
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# We reuse bitops from Nim standard lib, and expand it for multi-precision int.
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# MpInt rely on no undefined behaviour as often we scan 0. (if 1 is stored in a uint128 for example)
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# Also countLeadingZeroBits must return the size of the type and not 0 like in the stdlib
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func countLeadingZeroBits*(n: UintImpl): int {.inline.} =
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## Returns the number of leading zero bits in integer.
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const maxHalfRepr = bitsof(n) div 2
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let hi_clz = n.hi.countLeadingZeroBits
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result = if hi_clz == maxHalfRepr:
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n.lo.countLeadingZeroBits + maxHalfRepr
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else: hi_clz
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