Fix arb powers with integer exponents

Author: morluto

src/flint/test/test_arb.py

@@ -4,7 +4,7 @@
 
 import math
 
-from flint import arb, ctx
+from flint import arb, ctx, fmpz
 from flint.test.helpers import is_close_arb, raises
 
 def assert_almost_equal(x: float | int, y: float | int, places: int = 7) -> None:
@@ -295,6 +295,13 @@ def test_arb_arithmetic() -> None:
     assert (x ** 2) == arb(4)
     assert (2 ** x) == arb(4)
 
+    interval = arb(0, 1)
+    for exponent in (1, 2, fmpz(2)):
+        power = interval ** exponent
+        assert power.is_finite()
+        assert power.contains(0)
+        assert power.contains(1)
+
     assert raises(lambda: x + "bad", TypeError)  # type: ignore[operator]
     assert raises(lambda: "bad" + x, TypeError)  # type: ignore[operator]
     assert raises(lambda: x ** "bad", TypeError)  # type: ignore[operator]

src/flint/types/arb.pyx

@@ -6,7 +6,7 @@ from flint.flint_base.flint_context cimport thectx
 from flint.flint_base.flint_base cimport flint_scalar
 from flint.utils.typecheck cimport typecheck
 from flint.utils.conversion cimport chars_from_str, str_from_chars
-from flint.types.fmpz cimport fmpz_set_pylong
+from flint.types.fmpz cimport fmpz_set_any_ref, fmpz_set_pylong
 from flint.types.arf cimport arf
 from flint.types.fmpq cimport fmpq
 from flint.types.fmpz cimport fmpz
@@ -695,9 +695,18 @@ cdef class arb(flint_scalar):
 
     def __pow__(s, t, modulus):
         cdef arb_struct tval[1]
+        cdef fmpz_struct exponent[1]
         cdef int ttype
+        cdef int exponent_type
         if modulus is not None:
             raise TypeError("three-argument pow() not supported by arb type")
+        exponent_type = fmpz_set_any_ref(exponent, t)
+        if exponent_type != FMPZ_UNKNOWN:
+            u = arb.__new__(arb)
+            arb_pow_fmpz((<arb>u).val, (<arb>s).val, exponent, getprec())
+            if exponent_type == FMPZ_TMP:
+                fmpz_clear(exponent)
+            return u
         ttype = arb_set_any_ref(tval, t)
         if ttype == FMPZ_UNKNOWN:
             return NotImplemented