base32/64: decode in-place

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/coreutils/uudecode.c b/coreutils/uudecode.c
index 751976a87..10e5a55de 100644
--- a/coreutils/uudecode.c
+++ b/coreutils/uudecode.c
@@ -286,13 +286,19 @@ int baseNUM_main(int argc UNUSED_PARAM, char **argv)
         } else {
                 enum {
                         SRC_BUF_SIZE = 3 * 5 * 32, /* this *MUST* be a multiple of 3 and 5 */
-                        DST_BUF_SIZE = 4 * ((SRC_BUF_SIZE + 2) / 3),
+                        DST_BUF_SIZE = 8 * ((SRC_BUF_SIZE + 4) / 5), /* max growth on decode (base32 case) */
                 };
-                char src_buf[SRC_BUF_SIZE];
-                char dst_buf[DST_BUF_SIZE + 1];
-                int src_fd = fileno(src_stream);
-                int rem = 0;
+                /* Use one buffer for both input and output:
+                 * decoding reads input "left-to-right",
+                 * it's safe to place source at the end of the buffer and
+                 * overwrite it while decoding, just be careful to have a gap.
+                 */
+                char dst_buf[((DST_BUF_SIZE + /*gap:*/ 16) /*round up to 16:*/ | 0xf) + 1];
+#define src_buf (dst_buf + sizeof(dst_buf) - SRC_BUF_SIZE)
+                int src_fd, rem;
 
+                src_fd = fileno(src_stream);
+                rem = 0;
                 while (1) {
                         size_t size = full_read(src_fd, src_buf, SRC_BUF_SIZE);
                         if ((ssize_t)size < 0)
@@ -331,6 +337,7 @@ int baseNUM_main(int argc UNUSED_PARAM, char **argv)
                                 }
                         }
                 }
+#undef src_buf
         }
 
         fflush_stdout_and_exit(EXIT_SUCCESS);