bittest

Function: bittest
Section: conversions
C-Name: gbittest
Prototype: GL
Help: bittest(x,n): gives bit number n (coefficient of 2^n) of the integer x.
 Negative numbers behave as if modulo big power of 2.
Description:
 (small, small):bool:parens     ($(1)>>$(2))&1
 (int, small):bool              bittest($1, $2)
 (gen, small):gen               gbittest($1, $2)
Doc:
 outputs the $n^{\text{th}}$ bit of $x$ starting
 from the right (i.e.~the coefficient of $2^n$ in the binary expansion of $x$).
 The result is 0 or 1. For $x\ge1$, the highest 1-bit is at $n =
 \kbd{logint}(x)$ (and bigger $n$ gives $0$).
 \bprog
 ? bittest(7, 0)
 %1 = 1 \\ the bit 0 is 1
 ? bittest(7, 2)
 %2 = 1 \\ the bit 2 is 1
 ? bittest(7, 3)
 %3 = 0 \\ the bit 3 is 0
 @eprog\noindent
 See \secref{se:bitand} for the behavior at negative arguments.
Variant: For a \typ{INT} $x$, the variant \fun{long}{bittest}{GEN x, long n} is
 generally easier to use, and if furthermore $n\ge 0$ the low-level function
 \fun{ulong}{int_bit}{GEN x, long n} returns \kbd{bittest(abs(x),n)}.