add math.exp2 to python's math library

Author: Turreted

Misc/NEWS.d/next/Library/2021-11-28-17-24-11.bpo-45917.J5TIrd.rst

@@ -0,0 +1 @@
+Added :func:`math.exp2`:, which returns 2 raised to the power of x.

Modules/mathmodule.c

@@ -1248,6 +1248,9 @@ FUNC1A(erfc, m_erfc,
 FUNC1(exp, exp, 1,
       "exp($module, x, /)\n--\n\n"
       "Return e raised to the power of x.")
+FUNC1(exp2, exp2, 1,
+      "exp2($module, x, /)\n--\n\n"
+      "Return 2 raised to the power of x.")
 FUNC1(expm1, expm1, 1,
       "expm1($module, x, /)\n--\n\n"
       "Return exp(x)-1.\n\n"
@@ -3564,6 +3567,7 @@ static PyMethodDef math_methods[] = {
     {"erf",             math_erf,       METH_O,         math_erf_doc},
     {"erfc",            math_erfc,      METH_O,         math_erfc_doc},
     {"exp",             math_exp,       METH_O,         math_exp_doc},
+    {"exp2",            math_exp2,      METH_O,         math_exp2_doc},
     {"expm1",           math_expm1,     METH_O,         math_expm1_doc},
     {"fabs",            math_fabs,      METH_O,         math_fabs_doc},
     MATH_FACTORIAL_METHODDEF