~2x speedup using numba decorator in one single place

README.md

@@ -25,6 +25,17 @@ or:
 
 The cli project contains valid console script entrypoints for potrace. If you install the command-line package it will add `potracer` to your console scripts. Note the `-r` suffix so that it does not interfere with potrace that may be otherwise installed.
 
+### Numba (optional, experimental)
+[numba](https://github.com/numba/numba), an open source jit compiler for python & numpy, has been shown to speed up python potrace considerably (for complex images approx. a factor of 2).
+While numba supports most [platforms](https://numba.pydata.org/numba-doc/latest/user/installing.html#compatibility), it does not support _every_ platform that can run python.
+Depending on your requirements for runtime and depending on your platform, it might be worth to try.
+
+__By default, numba is disabled.__ Potrace with numba enabled can be installed with:
+
+* `pip install potracer[numba]`
+
+to make use of the speedup.
+
 # Requirements
 * numpy: for bitmap structures.
 

potrace/potrace.py

@@ -3,6 +3,14 @@
 
 import numpy as np
 
+try:
+    from numba import njit
+except ImportError:
+
+    def njit(*args, **kwargs):
+        return lambda f: f
+
+
 POTRACE_TURNPOLICY_BLACK = 0
 POTRACE_TURNPOLICY_WHITE = 1
 POTRACE_TURNPOLICY_LEFT = 2
@@ -641,6 +649,7 @@ def findpath(bm: np.array, x0: int, y0: int, sign: bool, turnpolicy: int) -> _Pa
     return _Path(pt, area, sign)
 
 
+@njit()
 def findnext(bm: np.array) -> Optional[Tuple[Union[int], int]]:
     """
     /* find the next set pixel in a row <= y. Pixels are searched first
@@ -1262,7 +1271,7 @@ def _calc_lon(pp: _Path) -> int:
         dk_y = sign(pt[k].y - pt[k1].y)
         cur_x = pt[k1].x - pt[i].x
         cur_y = pt[k1].y - pt[i].y
-        """find largest integer j such that xprod(constraint[0], cur+j*dk) >= 0 
+        """find largest integer j such that xprod(constraint[0], cur+j*dk) >= 0
         and xprod(constraint[1], cur+j*dk) <= 0. Use bilinearity of xprod. */"""
         a = xprod(constraint0x, constraint0y, cur_x, cur_y)
         b = xprod(constraint0x, constraint0y, dk_x, dk_y)

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = potracer
-version = 0.0.4
+version = 0.0.5
 description = Python Potrace
 long_description_content_type=text/markdown
 long_description = file: README.md

setup.py

@@ -5,5 +5,6 @@
     ],
     extras_require={
         'cli': ["potrace-cli"],
+        'numba': ["numba"],
     }
-)
+)