ls: fix -Q to match GNU

function                                             old     new   delta
print_name                                           137     229     +92
display_files                                        375     402     +27
c_escape_conv_str00                                    -      24     +24
display                                             1476    1485      +9
conv_str                                              33       -     -33
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 3/0 up/down: 152/-33)           Total: 119 bytes

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

2 files changed, 39 insertions, 20 deletions

diff --git a/libbb/c_escape.c b/libbb/c_escape.c
new file mode 100644
index 000000000..6c109f2e0
--- /dev/null
+++ b/libbb/c_escape.c
@@ -0,0 +1,20 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Copyright (C) 2025 by Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//kbuild:lib-y += c_escape.o
+
+#include "libbb.h"
+
+const char c_escape_conv_str00[] ALIGN1 =
+        "\\""0""\0" // [0]:00
+        "\\""a""\0" // [1]:07
+        "\\""b""\0" // [2]:08
+        "\\""t""\0" // [3]:09
+        "\\""n""\0" // [4]:0a
+        "\\""v""\0" // [5]:0b
+        "\\""f""\0" // [6]:0c
+        "\\""r"     // [7]:0d
+        ;
diff --git a/libbb/dump.c b/libbb/dump.c
index ac5d47d9e..0cc7775d6 100644
--- a/libbb/dump.c
+++ b/libbb/dump.c
@@ -478,37 +478,36 @@ static void bpad(PR *pr)
                 continue;
 }
 
-static const char conv_str[] ALIGN1 =
-        "\0"  "\\""0""\0"
-        "\007""\\""a""\0"
-        "\b"  "\\""b""\0"
-        "\f"  "\\""f""\0"
-        "\n"  "\\""n""\0"
-        "\r"  "\\""r""\0"
-        "\t"  "\\""t""\0"
-        "\v"  "\\""v""\0"
-        ;
-
 static void conv_c(PR *pr, unsigned char *p)
 {
-        const char *str = conv_str;
-
-        do {
-                if (*p == *str) {
-                        ++str;
-                        goto strpr; /* map e.g. '\n' to "\\n" */
-                }
-                str += 4;
-        } while (*str);
+        const char *str;
+        unsigned char ch;
+
+        ch = *p;
+        if (ch == 0 || (ch -= 6, (signed char)ch > 0 && ch <= 7)) {
+                /* map chars 0,7..13 to "\0","\{a,b,t,n,v,f,r}" */
+                str = c_escape_conv_str00 + 3 * ch;
+                goto strpr;
+        }
 
         if (isprint_asciionly(*p)) {
                 *pr->cchar = 'c';
                 printf(pr->fmt, *p);
         } else {
+#if 1
                 char buf[4];
                 /* gcc-8.0.1 needs lots of casts to shut up */
                 sprintf(buf, "%03o", (unsigned)(uint8_t)*p);
                 str = buf;
+#else // use faster version? +20 bytes of code
+                char buf[4];
+                buf[3] = '\0';
+                ch = *p;
+                buf[2] = '0' + (ch & 7); ch >>= 3;
+                buf[1] = '0' + (ch & 7); ch >>= 3;
+                buf[0] = '0' + ch;
+                str = buf;
+#endif
  strpr:
                 *pr->cchar = 's';
                 printf(pr->fmt, str);