Reference · Math

math.log2

math.log2(num) -> float

What it does

The logarithm of a number to base 2, as a float, as Python's math.log2. It is exact for a power of two, and elsewhere a digit closer than math.log(x, 2), which divides two logarithms. The number must be above zero.

Examples

print(math.log2(8), math.log2(1024), math.log2(0.5))print(math.log2(10), math.log2(3))

3.0 10.0 -1.03.321928094887362 1.584962500721156

Edge cases

• A power of two gives a whole float: math.log2(1024) is 10.0. For other numbers math.log(x, 2) can differ in the last digit.
• A number between 0 and 1 gives a negative answer; the smallest positive float is fine.
• inf gives inf, NaN gives NaN.
• The number of bits in a positive int is math.floor(math.log2(n)) + 1.

print(math.log2(1024), math.log(1024, 2))print(math.log2(10), math.log(10, 2))print(math.log2(0.25), math.log2(5e-324))print(math.log2(math.inf), math.log2(math.nan))print(math.floor(math.log2(1024)) + 1, math.floor(math.log2(1023)) + 1)

10.0 10.03.321928094887362 3.3219280948873626-2.0 -1074.0inf NaN11 10

Errors

Zero or a negative number is a runtime error (a domain error), not an error value: it stops the request, and ?? does not catch it. A value that is not a number is a runtime error too.

print(math.log2(0))

line 1: `math.log2`: math domain error (0)

print(math.log2(-8))

line 1: `math.log2`: math domain error (-8)

Chaining

print(256 | math.log2)print([1, 2, 4, 8] | map(math.log2))print(10 | math.exp2 | math.log2)

8.0[0.0, 1.0, 2.0, 3.0]10.0

See also

math.log, math.log10, math.exp2, math.frexp

Edit this page on GitHub · every example's output was made by running it (tools/refcheck.mjs) · questions on Discord or r/quillo