7f76914b74
Reexports of `amaranth.utils` functions are removed from `amaranth._utils` to avoid a circular import issue (for `deprecated`). Since this is a private module, this should not be a problem.
51 lines
1.3 KiB
Python
51 lines
1.3 KiB
Python
import operator
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from ._utils import deprecated
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__all__ = ["ceil_log2", "exact_log2", "log2_int", "bits_for"]
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def ceil_log2(n):
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"""Returns the integer log2 of the smallest power-of-2 greater than or equal to `n`.
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Raises a `ValueError` for negative inputs."""
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n = operator.index(n)
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if n < 0:
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raise ValueError("{n} is negative")
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if n == 0:
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return 0
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return (n - 1).bit_length()
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def exact_log2(n):
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"""Returns the integer log2 of `n`, which must be an exact power of two.
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Raises a `ValueError` if `n` is not a power of two."""
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n = operator.index(n)
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if n <= 0 or (n & (n - 1)):
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raise ValueError("{n} is not a power of 2")
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return (n - 1).bit_length()
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@deprecated("instead of `log2_int(n, True)`, use `exact_log2(n)`; instead of `log2_int(n, False)` use `ceil_log2(n)`")
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def log2_int(n, need_pow2=True):
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n = operator.index(n)
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if n == 0:
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return 0
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r = (n - 1).bit_length()
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if need_pow2 and (1 << r) != n:
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raise ValueError(f"{n} is not a power of 2")
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return r
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def bits_for(n, require_sign_bit=False):
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n = operator.index(n)
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if n > 0:
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r = ceil_log2(n + 1)
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else:
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require_sign_bit = True
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r = ceil_log2(-n)
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if require_sign_bit:
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r += 1
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return r
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