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15 def log2(x): 16 try: 17 return math.log(x, 2) 18 except ValueError: 19 return float("nan")

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14 def log2 (x): 15 return math.log (x, 2)

65 def log2(x): 66 """ Take log base 2 of x. 67 """ 68 x = _fix_real_lt_zero(x) 69 return nx.log(x)/_ln2

34 def log2(val): 35 """ 36 Calculate the log base 2 of a value. 37 """ 38 return int(math.log(val, 2))

340 def log2(x): 341 """ 342 Compute the logarithm base 2 of `x`. 343 344 Return the "principal value" (for a description of this, see 345 `numpy.log2`) of :math:`log_2(x)`. For real `x > 0`, this is 346 a real number (``log2(0)`` returns ``-inf`` and ``log2(np.inf)`` returns 347 ``inf``). Otherwise, the complex principle value is returned. 348 349 Parameters 350 ---------- 351 x : array_like 352 The value(s) whose log base 2 is (are) required. 353 354 Returns 355 ------- 356 out : ndarray or scalar 357 The log base 2 of the `x` value(s). If `x` was a scalar, so is `out`, 358 otherwise an array is returned. 359 360 See Also 361 -------- 362 numpy.log2 363 364 Notes 365 ----- 366 For a log2() that returns ``NAN`` when real `x < 0`, use `numpy.log2` 367 (note, however, that otherwise `numpy.log2` and this `log2` are 368 identical, i.e., both return ``-inf`` for `x = 0`, ``inf`` for `x = inf`, 369 and, notably, the complex principle value if ``x.imag != 0``). 370 371 Examples 372 -------- 373 We set the printing precision so the example can be auto-tested: 374 375 >>> np.set_printoptions(precision=4) 376 377 >>> np.emath.log2(8) 378 3.0 379 >>> np.emath.log2([-4, -8, 8]) 380 array([ 2.+4.5324j, 3.+4.5324j, 3.+0.j ]) 381 382 """ 383 x = _fix_real_lt_zero(x) 384 return nx.log2(x)

9 def log2(x): 10 return math.log(x)/math.log(2.)

112 def exact_log2(number): 113 """Find and return an unsigned integer i >= 0 such that ``number == 2**i``. If 114 no such integer exists, this function raises ValueError. 115 116 .. NOTE: 117 It essentially answers this question: 118 119 "How many times would you have to multiply 2 into itself to 120 get the given number?" 121 122 Taken from PyCrypto. 123 124 :param number: 125 Unsigned integer. 126 :returns: 127 An integer i >= 0 such that number == 2**i. 128 """ 129 num = number 130 if num <= 0: 131 raise ValueError("Cannot compute logarithm of non-positive integer") 132 i = 0 133 while num: 134 if (num & 1) and num != 1: 135 raise ValueError("No solution could be found") 136 i += 1 137 num >>= 1 138 i -= 1 139 #assert number == (1 << i) 140 return i