add math_utils submodule containing power for static integers

measuremancer/math_utils.nim

@@ -0,0 +1,43 @@
+import std / macros
+
+# Taken from `unchained`. This won't be exported from `measuremancer` though,
+# rather we will `bind` in the scope in which we use this.
+macro power*(x: typed, num: static int): untyped =
+  ## general purpose power using `^` for integers, which works for any
+  ## type by rewriting to a product of `*`.
+  ##
+  ## For the special cases of -1, 0, 1 we simply rewrite to the correct
+  ## result. Negative powers are written as `1 / x^p`
+  if num == 0:
+    result = quote do:
+      `x` * typeof(`x`)(0.0)
+  elif num == 1:
+    result = x
+  elif num == -1:
+    ## Assume that the type supports addition by a float!
+    result = quote do:
+      1.0 / `x`
+  else:
+    result = nnkInfix.newTree(ident"*")
+
+    proc addInfix(n, x: NimNode, num: int) =
+      var it = n
+      if num > 0:
+        it.add nnkInfix.newTree(ident"*")
+        it[1].addInfix(x, num - 1)
+      while it.len < 3:
+        it.add x
+
+    result.addInfix(x, abs(num) - 2)
+
+    # invert if num is negative
+    if num < -1:
+      ## Assume that the type supports addition by a float!
+      result = quote do:
+        1.0 / (`result`)
+
+import std/math
+proc power*[T](x: T, num: SomeInteger): T =
+  if num > 0: result = x ^ num
+  elif num == 0: result = T(1)
+  else: result = T(1) / (x ^ abs(num))