dd: support conv=swab

function                                             old     new   delta
dd_main                                             1482    1520     +38
static.conv_words                                     28      33      +5
packed_usage                                       29377   29375      -2

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

1 files changed, 23 insertions, 6 deletions

diff --git a/coreutils/dd.c b/coreutils/dd.c
index 9cb96bb06..1732a5c19 100644
--- a/coreutils/dd.c
+++ b/coreutils/dd.c
@@ -30,10 +30,10 @@
 //usage:     "\n        conv=noerror    Continue after read errors"
 //usage:     "\n        conv=sync       Pad blocks with zeros"
 //usage:     "\n        conv=fsync      Physically write data out before finishing"
+//usage:     "\n        conv=swab       Swap every pair of bytes"
 //usage:        )
 //usage:     "\n"
-//usage:     "\nNumbers may be suffixed by c (x1), w (x2), b (x512), kD (x1000), k (x1024),"
-//usage:     "\nMD (x1000000), M (x1048576), GD (x1000000000) or G (x1073741824)"
+//usage:     "\nN may be suffixed by c (1), w (2), b (512), kD (1000), k (1024), MD, M, GD, G"
 //usage:
 //usage:#define dd_example_usage
 //usage:       "$ dd if=/dev/zero of=/dev/ram1 bs=1M count=4\n"
@@ -155,9 +155,10 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
                 FLAG_SYNC    = 1 << 1,
                 FLAG_NOERROR = 1 << 2,
                 FLAG_FSYNC   = 1 << 3,
+                FLAG_SWAB    = 1 << 4,
                 /* end of conv flags */
-                FLAG_TWOBUFS = 1 << 4,
-                FLAG_COUNT   = 1 << 5,
+                FLAG_TWOBUFS = 1 << 5,
+                FLAG_COUNT   = 1 << 6,
         };
         static const char keywords[] ALIGN1 =
                 "bs\0""count\0""seek\0""skip\0""if\0""of\0"
@@ -167,7 +168,7 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
                 ;
 #if ENABLE_FEATURE_DD_IBS_OBS
         static const char conv_words[] ALIGN1 =
-                "notrunc\0""sync\0""noerror\0""fsync\0";
+                "notrunc\0""sync\0""noerror\0""fsync\0""swab\0";
 #endif
         enum {
                 OP_bs = 0,
@@ -185,11 +186,11 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
                 OP_conv_sync,
                 OP_conv_noerror,
                 OP_conv_fsync,
+                OP_conv_swab,
         /* Unimplemented conv=XXX: */
         //nocreat       do not create the output file
         //excl          fail if the output file already exists
         //fdatasync     physically write output file data before finishing
-        //swab          swap every pair of input bytes
         //lcase         change upper case to lower case
         //ucase         change lower case to upper case
         //block         pad newline-terminated records with spaces to cbs-size
@@ -197,6 +198,8 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
         //ascii         from EBCDIC to ASCII
         //ebcdic        from ASCII to EBCDIC
         //ibm           from ASCII to alternate EBCDIC
+        /* Partially implemented: */
+        //swab          swap every pair of input bytes: will abort on non-even reads
 #endif
         };
         int exitcode = EXIT_FAILURE;
@@ -377,6 +380,20 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
                          * conv=noerror just ignores input bad blocks */
                         n = 0;
                 }
+                if (flags & FLAG_SWAB) {
+                        /* If n is odd, last byte is not swapped:
+                         *  echo -n "qwe" | dd conv=swab bs=1
+                         * prints "wqe".
+                         * The code does not handle correctly odd-sized reads
+                         * in the *middle* of the input. FIXME.
+                         */
+                        uint16_t *p16 = (void*) ibuf;
+                        uint16_t *end = (void*) (ibuf + (n & ~(ssize_t)1));
+                        while (p16 < end) {
+                                *p16 = bswap_16(*p16);
+                                p16++;
+                        }
+                }
                 if ((size_t)n == ibs)
                         G.in_full++;
                 else {