From 558a753d3da5a2243a74b8d4e1c24044bdfb5c2e Mon Sep 17 00:00:00 2001
From: Keith Rothman <537074+litghost@users.noreply.github.com>
Date: Wed, 17 Feb 2021 10:18:24 -0800
Subject: [PATCH] Refactor "get only from iterator" to a utility.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>
---
 common/util.h                    | 23 +++++++++++++++++++++++
 fpga_interchange/arch.cc         |  7 ++-----
 fpga_interchange/arch.h          |  6 +++++-
 fpga_interchange/arch_pack_io.cc |  8 ++------
 4 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/common/util.h b/common/util.h
index 07ebac75..55718344 100644
--- a/common/util.h
+++ b/common/util.h
@@ -158,6 +158,29 @@ inline NetInfo *get_net_or_empty(CellInfo *cell, const IdString port)
         return nullptr;
 }
 
+// Get only value from a forward iterator begin/end pair.
+//
+// Generates assertion failure if std::distance(begin, end) != 1.
+template <typename ForwardIterator>
+inline const typename ForwardIterator::reference get_only_value(ForwardIterator begin, ForwardIterator end)
+{
+    NPNR_ASSERT(begin != end);
+    const typename ForwardIterator::reference ret = *begin;
+    ++begin;
+    NPNR_ASSERT(begin == end);
+    return ret;
+}
+
+// Get only value from a forward iterator range pair.
+//
+// Generates assertion failure if std::distance(r.begin(), r.end()) != 1.
+template <typename ForwardRange> inline auto get_only_value(ForwardRange r)
+{
+    auto b = r.begin();
+    auto e = r.end();
+    return get_only_value(b, e);
+}
+
 NEXTPNR_NAMESPACE_END
 
 #endif
diff --git a/fpga_interchange/arch.cc b/fpga_interchange/arch.cc
index 561f495d..cce93844 100644
--- a/fpga_interchange/arch.cc
+++ b/fpga_interchange/arch.cc
@@ -806,11 +806,8 @@ void Arch::map_cell_pins(CellInfo *cell, int32_t mapping) const
 void Arch::map_port_pins(BelId bel, CellInfo *cell) const
 {
     IdStringRange pins = getBelPins(bel);
-    NPNR_ASSERT(pins.begin() != pins.end());
-    auto b = pins.begin();
-    IdString pin = *b;
-    ++b;
-    NPNR_ASSERT(b == pins.end());
+    IdString pin = get_only_value(pins);
+
     NPNR_ASSERT(cell->ports.size() == 1);
     cell->cell_bel_pins[cell->ports.begin()->first].clear();
     cell->cell_bel_pins[cell->ports.begin()->first].push_back(pin);
diff --git a/fpga_interchange/arch.h b/fpga_interchange/arch.h
index 556aa566..1daf5526 100644
--- a/fpga_interchange/arch.h
+++ b/fpga_interchange/arch.h
@@ -656,7 +656,11 @@ struct BelPinRange
     BelPinIterator end() const { return e; }
 };
 
-struct IdStringIterator
+struct IdStringIterator : std::iterator<std::forward_iterator_tag,
+                                        /*T=*/IdString,
+                                        /*Distance=*/ptrdiff_t,
+                                        /*pointer=*/IdString *,
+                                        /*reference=*/IdString>
 {
     const int32_t *cursor;
 
diff --git a/fpga_interchange/arch_pack_io.cc b/fpga_interchange/arch_pack_io.cc
index 8a0fdc05..6a0ffe0b 100644
--- a/fpga_interchange/arch_pack_io.cc
+++ b/fpga_interchange/arch_pack_io.cc
@@ -20,6 +20,7 @@
 
 #include "log.h"
 #include "nextpnr.h"
+#include "util.h"
 
 NEXTPNR_NAMESPACE_BEGIN
 
@@ -235,12 +236,7 @@ void Arch::pack_ports()
         placed_cells.emplace(port_cell);
 
         IdStringRange package_bel_pins = getBelPins(package_bel);
-        // NPNR_ASSERT(std::distance(package_bel_pins.begin(), package_bel_pins.end()) == 1);
-        IdStringIterator b = package_bel_pins.begin();
-        NPNR_ASSERT(b != package_bel_pins.end());
-        ++b;
-        NPNR_ASSERT(b == package_bel_pins.end());
-        IdString pad_pin = *package_bel_pins.begin();
+        IdString pad_pin = get_only_value(package_bel_pins);
 
         WireId pad_wire = getBelPinWire(package_bel, pad_pin);
         place_iobufs(pad_wire, ports[port_pair.first].net, tightly_attached_bels, &placed_cells);