add scratch arena to Proc

1 files changed, 36 insertions, 0 deletions

diff --git a/doc/xar.txt b/doc/xar.txt
new file mode 100644
index 0000000..548827a
--- /dev/null
+++ b/doc/xar.txt
@@ -0,0 +1,36 @@
+/* andrew reese's Exponential Array datatype */
+
+use bits, mem.Arena, mem.arena_alloc
+
+const XAR_INIT_SZ = 8
+const XAR_MAX_DOUBLE = 20
+
+struct Xar(T) {
+	n u32,
+	chunk [XAR_MAX_DOUBLE]^T
+}
+
+#[inline]
+func xar_chnk_slot(xar ^Xar(T), idx u32) (u32, u32) {
+	let chnk = 31 - bits.clz((idx / XAR_INIT_SZ) + 1)
+	let slot = idx - ((XAR_INIT_SZ << chnk) - XAR_INIT_SZ)
+	return (chnk, slot)
+}
+
+func xar_get(xar ^Xar(T), idx u32) ^T {
+	let chnk, slot = xar_chnk_slot(xar, idx)
+	return xar->chunk[chnk] + (slot * sizeof(T))
+}
+
+func xar_put(xar ^Xar(T), idx u32, a ^Arena) {
+	let chnk, slot = xar_chnk_slot(xar, idx)
+	if (!xar->chunk[chnk]) {
+		xar->chunk[chnk] := arena_alloc(a, sizeof(T) * (XAR_INIT_SZ << chnk)), alignof(T))
+	}
+	return xar->chunk[chnk] + (slot * sizeof(T))
+}
+
+proc xar_push(xar ^Xar(T), v T, a ^Arena) {
+	xar_put(xar, xar.n, a)^ = v
+	xar.n := xar.n + 1
+}