From 232fcde308ae018764e5d54945a807d6a8097b0f Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 30 Apr 2017 22:59:37 -0700
Subject: ffi: support anonymous padding in structs.

If the ffi struct type operator specifies nil as a slot name,
then we treat the member as anonymous padding. When reading a
struct from a buffer, we skip the padding. When writing out a
struct to a buffer, we generate zeros in the size of the
anonymous member. The type of the member is ignored, except
for calculating the size.

* ffi.c (ffi_struct_put): If the slot name is nil, don't
recursively call put; just use memset to fill the target
with zero bytes.
(ffi_struct_get, ffi_struct_fill): If the slot name is
nil, don't call get to fetch data. Just skip the area.
---
 ffi.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/ffi.c b/ffi.c
index 272ea9d7..e9c95f48 100644
--- a/ffi.c
+++ b/ffi.c
@@ -963,11 +963,15 @@ static void ffi_struct_put(struct txr_ffi_type *tft, val strct, mem_t *dst,
   while (slots) {
     val slsym = pop(&slots);
     val type = pop(&types);
-    val slval = slot(strct, slsym);
     struct txr_ffi_type *mtft = ffi_type_struct(type);
     ucnum almask = mtft->align - 1;
     offs = (offs + almask) & ~almask;
-    mtft->put(mtft, slval, dst + offs, rtvec, self);
+    if (slsym) {
+      val slval = slot(strct, slsym);
+      mtft->put(mtft, slval, dst + offs, rtvec, self);
+    } else {
+      memset(dst + offs, 0, mtft->size);
+    }
     offs += mtft->size;
   }
 }
@@ -985,10 +989,11 @@ static val ffi_struct_get(struct txr_ffi_type *tft, mem_t *src, val self)
     val type = pop(&types);
     struct txr_ffi_type *mtft = ffi_type_struct(type);
     ucnum almask = mtft->align - 1;
-    val slval;
     offs = (offs + almask) & ~almask;
-    slval = mtft->get(mtft, src + offs, self);
-    slotset(strct, slsym, slval);
+    if (slsym) {
+      val slval = mtft->get(mtft, src + offs, self);
+      slotset(strct, slsym, slval);
+    }
     offs += mtft->size;
   }
 
@@ -1009,8 +1014,10 @@ static void ffi_struct_fill(struct txr_ffi_type *tft, mem_t *src,
     ucnum almask = mtft->align - 1;
     val slval;
     offs = (offs + almask) & ~almask;
-    slval = mtft->get(mtft, src + offs, self);
-    slotset(strct, slsym, slval);
+    if (slsym) {
+      slval = mtft->get(mtft, src + offs, self);
+      slotset(strct, slsym, slval);
+    }
     offs += mtft->size;
   }
 }
-- 
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