String: performance improvement converting uint64_t to string (4x)

Based on the trick given by A. Alexandrescu on Facebook Engineering
blog, this patch replace the old mk_str_itop() with the faster
algorithm proposed.

More details about the implementation here:

 https://www.facebook.com/notes/facebook-engineering/three-optimization-tips-for-c/10151361643253920

Signed-off-by: Eduardo Silva <eduardo@monkey.io>

include/monkey/mk_plugin.h

@@ -208,7 +208,7 @@ struct plugin_api
     char *(*pointer_to_buf) (mk_ptr_t);
 
     /* string functions */
-    int   (*str_itop) (int, mk_ptr_t *);
+    int   (*str_itop) (uint64_t, mk_ptr_t *);
     int   (*str_search) (const char *, const char *, int);
     int   (*str_search_n) (const char *, const char *, int, int);
     char *(*str_build) (char **, unsigned long *, const char *, ...) PRINTF_WARNINGS(3,4);

include/monkey/mk_string.h

@@ -20,9 +20,10 @@
 #ifndef MK_STR_H
 #define MK_STR_H
 
-#include "mk_memory.h"
-#include "mk_list.h"
-#include "mk_macros.h"
+#include <stdint.h>
+#include <monkey/mk_memory.h>
+#include <monkey/mk_list.h>
+#include <monkey/mk_macros.h>
 
 /* Case sensitive OFF */
 #define MK_STR_SENSITIVE 0
@@ -58,7 +59,7 @@ void mk_string_split_free(struct mk_list *list);
 int mk_string_trim(char **str);
 char *mk_string_build(char **buffer, unsigned long *len,
                       const char *format, ...) PRINTF_WARNINGS(3,4);
-int mk_string_itop(int n, mk_ptr_t *p);
+int mk_string_itop(uint64_t value, mk_ptr_t *p);
 char *mk_string_copy_substr(const char *string, int pos_init, int pos_end);
 
 char *mk_string_tolower(const char *in);

src/mk_signals.c

@@ -117,13 +117,9 @@ static void mk_signal_handler(int signo, siginfo_t *si, void *context UNUSED_PAR
 #endif
         mk_err("%s (%d), code=%d, addr=%p",
                strsignal(signo), signo, si->si_code, si->si_addr);
-
-        struct sched_list_node *sched;
-        sched = mk_sched_get_thread_conf();
-        printf("sched=%p\n", sched);
         //close(sched->server_fd);
-        pthread_exit(NULL);
-        //abort();
+        //pthread_exit(NULL);
+        abort();
     default:
         /* let the kernel handle it */
         kill(getpid(), signo);

src/mk_string.c

@@ -327,30 +327,64 @@ int mk_string_trim(char **str)
     return 0;
 }
 
-int mk_string_itop(int value, mk_ptr_t *p)
-{
-    char aux;
-    char *wstr = p->data;
-    char *begin, *end;
-    unsigned int uvalue = (value < 0) ? -value : value;
-
-    do *wstr++ = (char)(48 + (uvalue % 10)); while(uvalue /= 10);
-    if (value < 0) *wstr++ = '-';
-    *wstr='\0';
+uint32_t digits10(uint64_t v) {
+    if (v < 10) return 1;
+    if (v < 100) return 2;
+    if (v < 1000) return 3;
+    if (v < 1000000000000UL) {
+        if (v < 100000000UL) {
+            if (v < 1000000) {
+                if (v < 10000) return 4;
+                return 5 + (v >= 100000);
+            }
+            return 7 + (v >= 10000000UL);
+        }
+        if (v < 10000000000UL) {
+            return 9 + (v >= 1000000000UL);
+        }
+        return 11 + (v >= 100000000000UL);
+    }
+    return 12 + digits10(v / 1000000000000UL);
+}
 
-    begin = p->data;
-    end = wstr - 1;
+int mk_string_itop(uint64_t value, mk_ptr_t *p)
+{
+    static const char digits[201] =
+        "0001020304050607080910111213141516171819"
+        "2021222324252627282930313233343536373839"
+        "4041424344454647484950515253545556575859"
+        "6061626364656667686970717273747576777879"
+        "8081828384858687888990919293949596979899";
+
+    uint32_t const length = digits10(value);
+    uint32_t next = length - 1;
+    char *dst = p->data;
+
+    while (value >= 100) {
+        int const i = (value % 100) * 2;
+        value /= 100;
+        dst[next] = digits[i + 1];
+        dst[next - 1] = digits[i];
+        next -= 2;
+    }
 
-    while (end > begin) {
-        aux = *end, *end-- = *begin, *begin++ = aux;
+    /* Handle last 1-2 digits */
+    if (value < 10) {
+        dst[next] = '0' + (uint32_t) value;
+    }
+    else {
+        int i = (uint32_t) value * 2;
+        dst[next] = digits[i + 1];
+        dst[next - 1] = digits[i];
     }
 
-    *wstr++ = '\r';
-    *wstr++ = '\n';
-    *wstr++ = '\0';
+    dst = p->data + length;
+    *dst++ = '\r';
+    *dst++ = '\n';
+    *dst++ = '\0';
 
-    p->len = (wstr - p->data - 1);
-    return 0;
+    p->len = (dst - p->data - 1);
+    return p->len;
 }
 
 /* Return a buffer with a new string from string */