libsframe: reuse static function sframe_decoder_get_funcdesc_at_index

sframe_decoder_get_funcdesc_at_index () is the function to access SFrame
FDEs in the SFrame decoder context.  Use it consistently.

Avoid unnecessary type cast and include minor enhancements as the code
is moved around.

libsframe/
	* sframe.c (sframe_decoder_get_funcdesc_at_index): Move some
	checks here.  Move the static function definition before the new
	use.
	(sframe_decoder_get_funcdesc): Use
	sframe_decoder_get_funcdesc_at_index instead.

libsframe/sframe.c

@@ -341,6 +341,27 @@ sframe_fre_entry_size (sframe_frame_row_entry *frep, unsigned int fre_type)
 	  + sframe_fre_offset_bytes_size (fre_info));
 }
 
+/* Get the function descriptor entry at index FUNC_IDX in the decoder
+   context CTX.  */
+
+static sframe_func_desc_entry *
+sframe_decoder_get_funcdesc_at_index (sframe_decoder_ctx *ctx,
+				      uint32_t func_idx)
+{
+  sframe_func_desc_entry *fdep;
+  unsigned int num_fdes;
+  int err;
+
+  num_fdes = sframe_decoder_get_num_fidx (ctx);
+  if (num_fdes == 0
+      || func_idx >= num_fdes
+      || ctx->sfd_funcdesc == NULL)
+    return sframe_ret_set_errno (&err, SFRAME_ERR_DCTX_INVAL);
+
+  fdep = &ctx->sfd_funcdesc[func_idx];
+  return fdep;
+}
+
 static int
 flip_fre (char *fp, unsigned int fre_type, size_t *fre_size)
 {
@@ -1103,20 +1124,17 @@ sframe_decoder_get_funcdesc (sframe_decoder_ctx *ctx,
 			     unsigned char *func_info)
 {
   sframe_func_desc_entry *fdp;
-  unsigned int num_fdes;
   int err = 0;
 
   if (ctx == NULL || func_start_address == NULL || num_fres == NULL
       || func_size == NULL)
     return sframe_set_errno (&err, SFRAME_ERR_INVAL);
 
-  num_fdes = sframe_decoder_get_num_fidx (ctx);
-  if (num_fdes == 0
-      || i >= num_fdes
-      || ctx->sfd_funcdesc == NULL)
-    return sframe_set_errno (&err, SFRAME_ERR_DCTX_INVAL);
+  fdp = sframe_decoder_get_funcdesc_at_index (ctx, i);
+
+  if (fdp == NULL)
+    return sframe_set_errno (&err, SFRAME_ERR_FDE_NOTFOUND);
 
-  fdp = (sframe_func_desc_entry *) ctx->sfd_funcdesc + i;
   *num_fres = fdp->sfde_func_num_fres;
   *func_start_address = fdp->sfde_func_start_address;
   *func_size = fdp->sfde_func_size;
@@ -1125,22 +1143,6 @@ sframe_decoder_get_funcdesc (sframe_decoder_ctx *ctx,
   return 0;
 }
 
-/* Get the function descriptor entry at index FUNC_IDX in the decoder
-   context CTX.  */
-
-static sframe_func_desc_entry *
-sframe_decoder_get_funcdesc_at_index (sframe_decoder_ctx *ctx,
-				      uint32_t func_idx)
-{
-  /* Invalid argument.  No FDE will be found.  */
-  if (func_idx >= sframe_decoder_get_num_fidx (ctx))
-    return NULL;
-
-  sframe_func_desc_entry *fdep;
-  fdep = (sframe_func_desc_entry *) ctx->sfd_funcdesc;
-  return fdep + func_idx;
-}
-
 /* Get the FRE_IDX'th FRE of the function at FUNC_IDX'th function
    descriptor entry in the SFrame decoder CTX.  Returns error code as
    applicable.  */