From c50630989e80048a1e782d92e2642e760d35c2ed Mon Sep 17 00:00:00 2001
From: Alex Anderson <anderson.john.alexander@gmail.com>
Date: Mon, 8 Jul 2024 12:08:57 -0700
Subject: [PATCH] draft: add countingsort.c3 (#1230)

Draft countingsort.c3
---
 lib/std/sort/countingsort.c3 | 172 +++++++++++++++++++++++++++++++++++
 1 file changed, 172 insertions(+)
 create mode 100644 lib/std/sort/countingsort.c3

diff --git a/lib/std/sort/countingsort.c3 b/lib/std/sort/countingsort.c3
new file mode 100644
index 000000000..99a707761
--- /dev/null
+++ b/lib/std/sort/countingsort.c3
@@ -0,0 +1,172 @@
+module std::sort;
+import std::sort::is;
+import std::sort::cs;
+import std::sort::qs;
+
+/**
+ * Sort list using the counting sort algorithm.
+ * @require $defined(list[0]) && $defined(list.len) "The list must be indexable and support .len or .len()"
+ * @require $or(@typeid(key) == void*.typeid, @is_keyer(key, list)) "Expected a transformation function which returns a key-like type, think integral types"
+ **/
+macro countingsort(list, key = null) @builtin
+{
+	var $Type = $typeof(list);
+	var $KeyFuncType = $typeof(key);
+	usz len = sort::@len_from_list(list);
+	cs::csort(<$Type, $KeyFuncType>)(list, 0, len, key, ~((uint)0));
+}
+
+macro insertionsort_indexed(list, start, end, cmp = null) @builtin
+{
+	var $Type = $typeof(list);
+	var $CmpFuncType = $typeof(cmp);
+	is::isort(<$Type, $CmpFuncType>)(list, (usz)start, (usz)end, cmp);
+}
+
+macro quicksort_indexed(list, start, end, cmp = null) @builtin
+{
+	var $Type = $typeof(list);
+	var $CmpFuncType = $typeof(cmp);
+	qs::qsort(<$Type, $CmpFuncType>)(list, (isz)start, (isz)(end-1), cmp);
+}
+
+module std::sort::cs(<Type, Keyer>);
+
+def Counts = ulong[256] @private;
+def Ranges = ulong[257] @private;
+def Indexs = char[256] @private;
+def ElementType = $typeof(Type{}[0]);
+//def KeyerReturnTypeid = $typeof(Keyer.returns); //Keyer{}(Keyer.params[0]{})
+def KeyerReturnType = $evaltype(Keyer.returns.qnameof);
+def CmpCallback     = fn bool(ElementType*, ElementType*);
+
+fn void csort(Type list, usz low, usz high, Keyer key, uint byte_idx)
+{
+	var $no_key = Keyer.typeid == void*.typeid;
+    var $key_by_value = $and(!$no_key, Keyer.params[0] == @typeid(list[0]));
+    var $list_has_get_ref = $defined(list.get_ref(0));
+
+    byte_idx = byte_idx >= KeyerReturnType.sizeof ? KeyerReturnType.sizeof-1 : byte_idx;
+	
+	if (high <= low) {
+		return;
+	}
+
+	Counts counts;
+	Ranges ranges;
+	Indexs indexs;
+
+	KeyerReturnType mn = ~((KeyerReturnType)0);
+	KeyerReturnType mx = (KeyerReturnType)0;
+
+	char last_key = 0;
+	char keys_ordered = 1;
+
+	for (usz i = 0; i < 256; i++) {
+		counts[i] = 0;
+	}
+
+	for (usz i = low; i < high; i++) {
+		$if $list_has_get_ref:
+			$if $key_by_value:
+				KeyerReturnType k = key(*list.get_ref(i));
+			$else
+				KeyerReturnType k = key(list.get_ref(i));
+			$endif;
+
+
+		$else
+			$if $key_by_value:
+				KeyerReturnType k = key(list[i]);
+			$else
+				KeyerReturnType k = key(&list[i]);
+			$endif;
+		$endif
+
+		char key_byte = (char)((k >> (byte_idx*8)) & 0xff);
+		++counts[key_byte];
+
+		mn = k < mn ? k : mn;
+		mx = k > mx ? k : mx;
+
+		keys_ordered = keys_ordered & (char)(key_byte >= last_key); 
+		last_key     = key_byte;
+	}
+
+	KeyerReturnType diff = mx-mn;
+	if (diff == 0) {
+		return;
+	}
+
+	ushort parition_count = 0;
+	usz total = 0;
+	for (usz i = 0; i < 256; i++) {
+		usz count = counts[i];
+		indexs[parition_count] = (char)i;
+		parition_count += (ushort)(count > 0);
+		counts[i] = total;
+		ranges[i] = total;
+		total += count;
+	}
+	ranges[256] = total;
+	
+	if (!keys_ordered) {
+		usz sorted_count = 0;
+		//ElementType* first = list.first();
+		do {
+			for (usz x = 0; x < 256; x++) {
+				usz s = counts[x];
+				usz e = ranges[x + 1];
+
+				sorted_count += (e - s);
+				for (; s < e; s++) {
+					$if $list_has_get_ref:
+						$if $key_by_value:
+							KeyerReturnType k = key(*list.get_ref(low+s));
+						$else
+							KeyerReturnType k = key(list.get_ref(low+s));
+						$endif;
+						char k_idx = (char)(k >> (byte_idx*8));
+						usz          target_idx = counts[k_idx];
+
+						@swap(list[low+s], list[low+target_idx]);
+						counts[k_idx] += 1;
+					$else
+						$if $key_by_value:
+							KeyerReturnType k = key(list[low+s]);
+						$else
+							KeyerReturnType k = key(&list[low+s]);
+						$endif;
+						char k_idx = (char)(k >> (byte_idx*8));
+						usz          target_idx = counts[k_idx];
+
+						@swap(list[low+s], list[low+target_idx]);
+						counts[k_idx] += 1;
+					$endif;
+				}
+			}
+		} while (sorted_count < ranges[256]);
+	}
+
+	if (byte_idx) {
+		for (usz p = 0; p < parition_count; ++p) {
+			usz i = indexs[p];
+			usz	start_offset = ranges[i];
+			usz	end_offset   = ranges[i + 1];
+
+			usz	items        = end_offset - start_offset;
+
+			if (items <= 32) {
+				insertionsort_indexed(list, low+start_offset, low+end_offset, fn bool (ElementType* lhs, ElementType* rhs) {
+					return Keyer{}(lhs) < Keyer{}(rhs);
+				});
+			} else if (items <= 128) {
+				quicksort_indexed(list, low+start_offset, low+end_offset, fn long (ElementType* lhs, ElementType* rhs) {
+					return (long)(Keyer{}(lhs) - Keyer{}(rhs));
+				});
+			} else {
+				csort(list, low+start_offset, low+end_offset, key, byte_idx-1);
+			}
+		}
+	}
+}