lib/vsprintf.c: eliminate some branches

Since FORMAT_TYPE_INT is simply 1 more than FORMAT_TYPE_UINT, and
similarly for BYTE/UBYTE, SHORT/USHORT, LONG/ULONG, we can eliminate a few
instructions by making SIGN have the value 1 instead of 2, and then use
arithmetic instead of branches for computing the right spec->type.  It's a
little hacky, but certainly in the same spirit as SMALL needing to have
the value 0x20.  For example for the spec->qualifier == 'l' case, gcc now
generates

     75e:       0f b6 53 01             movzbl 0x1(%rbx),%edx
     762:       83 e2 01                and    $0x1,%edx
     765:       83 c2 09                add    $0x9,%edx
     768:       88 13                   mov    %dl,(%rbx)

instead of

     763:       0f b6 53 01             movzbl 0x1(%rbx),%edx
     767:       83 e2 02                and    $0x2,%edx
     76a:       80 fa 01                cmp    $0x1,%dl
     76d:       19 d2                   sbb    %edx,%edx
     76f:       83 c2 0a                add    $0xa,%edx
     772:       88 13                   mov    %dl,(%rbx)

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index b235c96167d32e80add7999f7833684abd54040b..318d583fe86267798fbf9fa6803b9cc7bf344b53 100644 (file)
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -340,8 +340,8 @@ int num_to_str(char *buf, int size, unsigned long long num)
        return len;
 }
 
-#define ZEROPAD        1               /* pad with zero */
-#define SIGN   2               /* unsigned/signed long */
+#define SIGN   1               /* unsigned/signed, must be 1 */
+#define ZEROPAD        2               /* pad with zero */
 #define PLUS   4               /* show plus */
 #define SPACE  8               /* space if plus */
 #define LEFT   16              /* left justified */
@@ -447,7 +447,7 @@ char *number(char *buf, char *end, unsigned long long num,
                spec.precision = i;
        /* leading space padding */
        spec.field_width -= spec.precision;
-       if (!(spec.flags & (ZEROPAD+LEFT))) {
+       if (!(spec.flags & (ZEROPAD | LEFT))) {
                while (--spec.field_width >= 0) {
                        if (buf < end)
                                *buf = ' ';
@@ -1738,29 +1738,21 @@ qualifier:
        if (spec->qualifier == 'L')
                spec->type = FORMAT_TYPE_LONG_LONG;
        else if (spec->qualifier == 'l') {
-               if (spec->flags & SIGN)
-                       spec->type = FORMAT_TYPE_LONG;
-               else
-                       spec->type = FORMAT_TYPE_ULONG;
+               BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG);
+               spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN);
        } else if (_tolower(spec->qualifier) == 'z') {
                spec->type = FORMAT_TYPE_SIZE_T;
        } else if (spec->qualifier == 't') {
                spec->type = FORMAT_TYPE_PTRDIFF;
        } else if (spec->qualifier == 'H') {
-               if (spec->flags & SIGN)
-                       spec->type = FORMAT_TYPE_BYTE;
-               else
-                       spec->type = FORMAT_TYPE_UBYTE;
+               BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE);
+               spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN);
        } else if (spec->qualifier == 'h') {
-               if (spec->flags & SIGN)
-                       spec->type = FORMAT_TYPE_SHORT;
-               else
-                       spec->type = FORMAT_TYPE_USHORT;
+               BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT);
+               spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN);
        } else {
-               if (spec->flags & SIGN)
-                       spec->type = FORMAT_TYPE_INT;
-               else
-                       spec->type = FORMAT_TYPE_UINT;
+               BUILD_BUG_ON(FORMAT_TYPE_UINT + SIGN != FORMAT_TYPE_INT);
+               spec->type = FORMAT_TYPE_UINT + (spec->flags & SIGN);
        }
 
        return ++fmt - start;