From 5c5e2c3075235079fda94fc6a159cc5275f85a0c Mon Sep 17 00:00:00 2001
From: Marc Glisse <marc.glisse@inria.fr>
Date: Wed, 6 May 2020 14:13:14 +0200
Subject: Refactor the numpy -> C++ range conversion

If we want to reuse it for bottleneck...
---
 src/python/gudhi/hera.cc | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/src/python/gudhi/hera.cc b/src/python/gudhi/hera.cc
index 63bbb075..5aec1806 100644
--- a/src/python/gudhi/hera.cc
+++ b/src/python/gudhi/hera.cc
@@ -22,7 +22,7 @@ namespace py = pybind11;
 typedef py::array_t<double> Dgm;
 
 // Get m[i,0] and m[i,1] as a pair
-auto pairify(void* p, ssize_t h, ssize_t w) {
+static auto pairify(void* p, ssize_t h, ssize_t w) {
   return [=](ssize_t i){
     char* birth = (char*)p + i * h;
     char* death = birth + w;
@@ -30,28 +30,29 @@ auto pairify(void* p, ssize_t h, ssize_t w) {
   };
 }
 
+inline auto numpy_to_range_of_pairs(py::array_t<double> dgm) {
+  py::buffer_info buf = dgm.request();
+  // shape (n,2) or (0) for empty
+  if((buf.ndim!=2 || buf.shape[1]!=2) && (buf.ndim!=1 || buf.shape[0]!=0))
+    throw std::runtime_error("Diagram must be an array of size n x 2");
+  // In the case of shape (0), avoid reading non-existing strides[1] even if we won't use it.
+  ssize_t stride1 = buf.ndim == 2 ? buf.strides[1] : 0;
+  auto cnt = boost::counting_range<ssize_t>(0, buf.shape[0]);
+  return boost::adaptors::transform(cnt, pairify(buf.ptr, buf.strides[0], stride1));
+  // Be careful that the returned range cannot contain references to dead temporaries.
+}
+
 double wasserstein_distance(
     Dgm d1, Dgm d2,
     double wasserstein_power, double internal_p,
     double delta)
 {
-  py::buffer_info buf1 = d1.request();
-  py::buffer_info buf2 = d2.request();
+  // I *think* the call to request() has to be before releasing the GIL.
+  auto diag1 = numpy_to_range_of_pairs(d1);
+  auto diag2 = numpy_to_range_of_pairs(d2);
 
   py::gil_scoped_release release;
 
-  // shape (n,2) or (0) for empty
-  if((buf1.ndim!=2 || buf1.shape[1]!=2) && (buf1.ndim!=1 || buf1.shape[0]!=0))
-    throw std::runtime_error("Diagram 1 must be an array of size n x 2");
-  if((buf2.ndim!=2 || buf2.shape[1]!=2) && (buf2.ndim!=1 || buf2.shape[0]!=0))
-    throw std::runtime_error("Diagram 2 must be an array of size n x 2");
-  ssize_t stride11 = buf1.ndim == 2 ? buf1.strides[1] : 0;
-  ssize_t stride21 = buf2.ndim == 2 ? buf2.strides[1] : 0;
-  auto cnt1 = boost::counting_range<ssize_t>(0, buf1.shape[0]);
-  auto diag1 = boost::adaptors::transform(cnt1, pairify(buf1.ptr, buf1.strides[0], stride11));
-  auto cnt2 = boost::counting_range<ssize_t>(0, buf2.shape[0]);
-  auto diag2 = boost::adaptors::transform(cnt2, pairify(buf2.ptr, buf2.strides[0], stride21));
-
   hera::AuctionParams<double> params;
   params.wasserstein_power = wasserstein_power;
   // hera encodes infinity as -1...
-- 
cgit v1.2.3