From 67700ced54e4a395444b13991fd230bb69558ccc Mon Sep 17 00:00:00 2001
From: Hans Goudey <h.goudey@me.com>
Date: Fri, 28 Apr 2023 16:14:03 +0200
Subject: [PATCH] BLI: Add "take front" and "take back" methods to bit spans

This is consistent with `Span`, and also allows returning a bounded
bit span when taking the front of an existing bounded span, which
can simplify using optimized bit processing.

Pull Request: https://projects.blender.org/blender/blender/pulls/107441
---
 .../blender/blenkernel/intern/mesh_mirror.cc  |  4 +--
 source/blender/blenlib/BLI_bit_span.hh        | 30 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/source/blender/blenkernel/intern/mesh_mirror.cc b/source/blender/blenkernel/intern/mesh_mirror.cc
index ca787acbbf5..8f94717b281 100644
--- a/source/blender/blenkernel/intern/mesh_mirror.cc
+++ b/source/blender/blenkernel/intern/mesh_mirror.cc
@@ -336,8 +336,8 @@ Mesh *BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(MirrorModifierData *mmd,
     const blender::BoundedBitSpan src = mesh->runtime->subsurf_optimal_display_edges;
     result->runtime->subsurf_optimal_display_edges.resize(result->totedge);
     blender::MutableBoundedBitSpan dst = result->runtime->subsurf_optimal_display_edges;
-    dst.slice({0, src.size()}).copy_from(src);
-    dst.slice({src.size(), src.size()}).copy_from(src);
+    dst.take_front(src.size()).copy_from(src);
+    dst.take_back(src.size()).copy_from(src);
   }
 
   /* handle uvs,
diff --git a/source/blender/blenlib/BLI_bit_span.hh b/source/blender/blenlib/BLI_bit_span.hh
index 36dbb91bc65..2e8088793df 100644
--- a/source/blender/blenlib/BLI_bit_span.hh
+++ b/source/blender/blenlib/BLI_bit_span.hh
@@ -110,6 +110,16 @@ class BitSpan {
     return {data_, bit_range_.slice(range)};
   }
 
+  BitSpan take_front(const int64_t n) const
+  {
+    return {data_, bit_range_.take_front(n)};
+  }
+
+  BitSpan take_back(const int64_t n) const
+  {
+    return {data_, bit_range_.take_back(n)};
+  }
+
   const BitInt *data() const
   {
     return data_;
@@ -195,6 +205,11 @@ class BoundedBitSpan : public BitSpan {
   {
     return bit_range_.size() & BitIndexMask;
   }
+
+  BoundedBitSpan take_front(const int64_t n) const
+  {
+    return {data_, bit_range_.take_front(n)};
+  }
 };
 
 /** Same as #BitSpan, but also allows modifying the referenced bits. */
@@ -237,6 +252,16 @@ class MutableBitSpan {
     return {data_, bit_range_.slice(range)};
   }
 
+  MutableBitSpan take_front(const int64_t n) const
+  {
+    return {data_, bit_range_.take_front(n)};
+  }
+
+  MutableBitSpan take_back(const int64_t n) const
+  {
+    return {data_, bit_range_.take_back(n)};
+  }
+
   BitInt *data() const
   {
     return data_;
@@ -331,6 +356,11 @@ class MutableBoundedBitSpan : public MutableBitSpan {
     return bit_range_.size() & BitIndexMask;
   }
 
+  MutableBoundedBitSpan take_front(const int64_t n) const
+  {
+    return {data_, bit_range_.take_front(n)};
+  }
+
   void copy_from(const BitSpan other);
   void copy_from(const BoundedBitSpan other);
 };