I have written a primitive function for exponentiation with integers as
power using the multiply-and-square algorithm.
For performance reasons I used primitive type hints for the arguments and
the return value.
Profiling the whole application I noticed that there are a lot of
java.lang.Double/valueOf calls.
Looking at the bytecode I see that in Clojure 1.3 as well as in Clojure 1.4
the result value gets boxed and unboxed like
Double.valueOf(result).doubleValue().
Am I doing something wrong? Is there a serious bug related to the support
of primitive functions?
The source code:
(defn first-bit?
{:inline (fn [n] `(== 1 (clojure.lang.Numbers/and ~n, 1)) )}
[^long n]
(== 1 (clojure.lang.Numbers/and n, 1)))
(defn exp-int
^double [^double x, ^long c]
(loop [result 1.0, factor x, c c]
(if (> c 0)
(recur
(if (first-bit? c)
(* result factor)
result),
(* factor factor),
(bit-shift-right c 1))
result)))
Last lines of the Java bytecode of `exp-int`:
59 dload 5; /* result */
61 invokestatic 40; /* java.lang.Double
java.lang.Double.valueOf(double c) */
64 checkcast 85; /* java.lang.Number */
67 invokevirtual 89; /* double doubleValue() */
70 dreturn;
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