MINOR: ist: add new function ist_find_range() to find a character range

This looks up the character range <min>..<max> in the input string and
returns a pointer to the first one found. It's essentially the equivalent
of ist_find_ctl() in that it searches by 32 or 64 bits at once, but deals
with a range.

diff --git a/include/import/ist.h b/include/import/ist.h
index 50df199f19ff99953c508d24d3f32bcdeb8105aa..16b86164ea38697a92c017587d449092a092ea59 100644 (file)
--- a/include/import/ist.h
+++ b/include/import/ist.h
@@ -747,6 +747,53 @@ static inline const char *ist_find_ctl(const struct ist ist)
        return NULL;
 }
 
+/* Returns a pointer to the first character found <ist> that belongs to the
+ * range [min:max] inclusive, or NULL if none is present. The function is
+ * optimized for strings having no such chars by processing up to sizeof(long)
+ * bytes at once on architectures supporting efficient unaligned accesses.
+ * Despite this it is not very fast (~0.43 byte/cycle) and should mostly be
+ * used on low match probability when it can save a call to a much slower
+ * function. Will not work for characters 0x80 and above. It's optimized for
+ * min and max to be known at build time.
+ */
+static inline const char *ist_find_range(const struct ist ist, unsigned char min, unsigned char max)
+{
+       const union { unsigned long v; } __attribute__((packed)) *u;
+       const char *curr = (void *)ist.ptr - sizeof(long);
+       const char *last = curr + ist.len;
+       unsigned long l1, l2;
+
+       /* easier with an exclusive boundary */
+       max++;
+
+       do {
+               curr += sizeof(long);
+               if (curr > last)
+                       break;
+               u = (void *)curr;
+               /* add 0x<min><min><min><min>..<min> then subtract
+                * 0x<max><max><max><max>..<max> to the value to generate a
+                * carry in the lower byte if the byte contains a lower value.
+                * If we generate a bit 7 that was not there, it means the byte
+                * was min..max.
+                */
+               l2  = u->v;
+               l1  = ~l2 & ((~0UL / 255) * 0x80); /* 0x808080...80 */
+               l2 += (~0UL / 255) * min;          /* 0x<min><min>..<min> */
+               l2 -= (~0UL / 255) * max;          /* 0x<max><max>..<max> */
+       } while ((l1 & l2) == 0);
+
+       last += sizeof(long);
+       if (__builtin_expect(curr < last, 0)) {
+               do {
+                       if ((unsigned char)(*curr - min) < (unsigned char)(max - min))
+                               return curr;
+                       curr++;
+               } while (curr < last);
+       }
+       return NULL;
+}
+
 /* looks for first occurrence of character <chr> in string <ist> and returns
  * the tail of the string starting with this character, or (ist.end,0) if not
  * found.