From c54df81f05e622bd3ce6daa0bc4ba5d3999f958d Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 11 Jun 2019 19:47:32 -0700
Subject: buffers: allow sub operation.

* buf.c (sub_buf): New function.

* buf.h (sub_buf): Declared.

* lib.c (sub): Hook in BUF type.
(replace): Diagnose BUF specially as unsupported.
---
 buf.c | 32 ++++++++++++++++++++++++++++++++
 buf.h |  1 +
 lib.c |  8 +++++++-
 3 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/buf.c b/buf.c
index 5e5a5d66..06fb0abf 100644
--- a/buf.c
+++ b/buf.c
@@ -239,6 +239,38 @@ void buf_fill(val buf, mem_t *src, val self)
   memcpy(b->data, src, c_num(b->len));
 }
 
+val sub_buf(val buf, val from, val to)
+{
+  struct buf *b = buf_handle(buf, lit("sub"));
+  val len = b->len;
+
+  if (null_or_missing_p(from))
+    from = zero;
+  else if (from == t)
+    from = len;
+  else if (lt(from, zero)) {
+    from = plus(from, len);
+    if (to == zero)
+      to = len;
+  }
+
+  if (null_or_missing_p(to) || to == t)
+    to = len;
+  else if (lt(to, zero))
+    to = plus(to, len);
+
+  from = max2(zero, min2(from, len));
+  to = max2(zero, min2(to, len));
+
+  if (ge(from, to)) {
+    return make_buf(zero, nil, zero);
+  } else if (from == 0 && to == len) {
+    return buf;
+  } else {
+    return make_duplicate_buf(minus(to, from), b->data + c_num(from));
+  }
+}
+
 static void buf_put_bytes(val buf, val pos, mem_t *ptr, cnum size, val self)
 {
   struct buf *b = buf_handle(buf, self);
diff --git a/buf.h b/buf.h
index 60004112..db83f2a3 100644
--- a/buf.h
+++ b/buf.h
@@ -37,6 +37,7 @@ val length_buf(val buf);
 val buf_alloc_size(val buf);
 mem_t *buf_get(val buf, val self);
 void buf_fill(val buf, mem_t *src, val self);
+val sub_buf(val seq, val from, val to);
 
 #if HAVE_I8
 val buf_put_i8(val buf, val pos, val num);
diff --git a/lib.c b/lib.c
index e3e1909e..1794fa99 100644
--- a/lib.c
+++ b/lib.c
@@ -9996,6 +9996,8 @@ val sub(val seq, val from, val to)
     return sub_str(seq, from, to);
   case VEC:
     return sub_vec(seq, from, to);
+  case BUF:
+    return sub_buf(seq, from, to);
   case COBJ:
     if (seq->co.cls == carray_s)
       return carray_sub(seq, from, to);
@@ -10097,6 +10099,8 @@ val refset(val seq, val ind, val newval)
 
 val replace(val seq, val items, val from, val to)
 {
+  val self = lit("replace");
+
   switch (type(seq)) {
   case NIL:
   case CONS:
@@ -10114,8 +10118,10 @@ val replace(val seq, val items, val from, val to)
     if (obj_struct_p(seq))
       return replace_obj(seq, items, from, to);
     /* fallthrough */
+  case BUF:
+    type_mismatch(lit("~a: operation doesn't support buf type"), self, nao);
   default:
-    type_mismatch(lit("replace: ~s is not a sequence"), seq, nao);
+    type_mismatch(lit("~a: ~s is not a sequence"), self, seq, nao);
   }
 }
 
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