Optimize is_diacritic

is_diacritic is used for pretty much all of the text display sizing
Timing here matters, so important it uses a
priority buffer in order to cut down on searching the database.

This patch is verified functionally equlivalent but
saves 80 bytes and is ~20% faster for the clip+ I tested it on

Several things were done:

Optimizing the copy loop for the priority buffer

Globbing some operations together

but the main one has to do with the database structure its self
--
Rather than a bit packed struct it combines the lower 8 bytes into
one value [info] and uses flags to access the values instead

Change-Id: I475073419b647639ef1eeaa3b9213e4e1067c0db

1 files changed, 29 insertions, 20 deletions

diff --git a/firmware/common/diacritic.c b/firmware/common/diacritic.c
index aa2726c5fb..eca7b07b6e 100644
--- a/firmware/common/diacritic.c
+++ b/firmware/common/diacritic.c
@@ -10,6 +10,7 @@
  * Copyright (C) 2009 Phinitnun Chanasabaeng
  *     Initial work
  * Copyright (C) 2009 Tomer Shalev
+ * Copyright (C) 2018 William Wilgus
  *
  * Rockbox diacritic positioning
  * Based on initial work by Phinitnun Chanasabaeng
@@ -27,19 +28,23 @@
 #include "system.h"
 
 #define DIAC_NUM_RANGES      (ARRAYLEN(diac_ranges))
+#define DIAC_RTL             (1 << 7)
+#define DIAC_CNT             (0xFF ^ DIAC_RTL)
 
 /* Each diac_range_ struct defines a Unicode range that begins with
  * N diacritic characters, and continues with non-diacritic characters up to the
- * base of the next item in the array */
+ * base of the next item in the array, [info] packs RTL status and the count of
+ * diacritic chars after [base]. RTL occupies the MSB and CNT the (7) lower bits
+ */
+
 struct diac_range
 {
-    unsigned base           : 16;
-    unsigned num_diacritics :  7;
-    unsigned is_rtl         :  1;
+    uint16_t base;
+    uint8_t  info; /* [RTL:1 CNT:7] */
 };
 
 #define DIAC_RANGE_ENTRY(first_diac, first_non_diac, is_rtl) \
-    { first_diac, first_non_diac - first_diac, is_rtl }
+ { first_diac, ((first_non_diac - first_diac) & DIAC_CNT) | (is_rtl * DIAC_RTL)}
 
 /* Sorted by Unicode value */
 static const struct diac_range diac_ranges[] =
@@ -190,22 +195,28 @@ static const struct diac_range diac_ranges[] =
 
 #define MRU_MAX_LEN 32
 
-static unsigned short mru_len = 0;
-static unsigned short diacritic_mru[MRU_MAX_LEN];
-
 bool is_diacritic(const unsigned short char_code, bool *is_rtl)
 {
-    unsigned short mru, i;
+    static uint8_t mru_len = 0;
+    static uint8_t diacritic_mru[MRU_MAX_LEN];
+
+    uint8_t i, itmp;
+    uint8_t info, mru;
+
     const struct diac_range *diac;
 
     /* Search in MRU */
-    for (mru = 0; mru < mru_len; mru++)
+    for (mru = 0, i = 0; mru < mru_len; mru++)
     {
+
+        /* Items shifted >> 1 */
+        itmp = i;
         i = diacritic_mru[mru];
+            diacritic_mru[mru] = itmp;
 
         /* Found in MRU */
-        if (diac_ranges[i].base <= char_code &&
-                char_code < diac_ranges[i + 1].base)
+        if ((char_code >= (diac = &diac_ranges[i])->base)
+         && (char_code < (++diac)->base))
         {
             goto Found;
         }
@@ -219,23 +230,21 @@ bool is_diacritic(const unsigned short char_code, bool *is_rtl)
             break;
     }
 
-    /* Add MRU entry, or overwrite LRU if MRU array is full */
+    /* Add MRU entry */
     if (mru_len < MRU_MAX_LEN)
         mru_len++;
-    else
-        mru--;
 
 Found:
+
     /* Promote MRU item to top of MRU */
-    for ( ; mru > 0; mru--)
-        diacritic_mru[mru] = diacritic_mru[mru - 1];
     diacritic_mru[0] = i;
 
     diac = &diac_ranges[i];
+    info = diac->info;
 
     /* Update RTL */
     if (is_rtl)
-        *is_rtl = diac->is_rtl;
+        *is_rtl = ((DIAC_RTL & info) == DIAC_RTL);
 
-    return (char_code < diac->base + diac->num_diacritics);
-}
+    return (char_code < diac->base + (info & DIAC_CNT));
+}
\ No newline at end of file