[LyX/master] Improve prediction of block outside covered areas

[Guillaume Munch]

commit dbcbf305b2525493b4dea2530af4f91fe7ca436c
Author: Guillaume Munch <g...@lyx.org>
Date:   Sun Dec 4 18:28:02 2016 +0100

    Improve prediction of block outside covered areas
---
 src/frontends/qt4/GuiSymbols.cpp |   17 ++++++++++++-----
 1 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/frontends/qt4/GuiSymbols.cpp b/src/frontends/qt4/GuiSymbols.cpp
index 9f7dd61..e2c0f04 100644
--- a/src/frontends/qt4/GuiSymbols.cpp
+++ b/src/frontends/qt4/GuiSymbols.cpp
@@ -152,6 +152,7 @@ const int no_blocks = sizeof(unicode_blocks) / 
sizeof(UnicodeBlocks);
 QString getBlock(char_type c)
 {
        // store an educated guess for the next search
+       // 0 <= lastBlock < no_blocks
        // FIXME THREAD
        static int lastBlock = 0;
 
@@ -159,10 +160,6 @@ QString getBlock(char_type c)
        if (c < 0x7f)
                lastBlock = 0;
 
-       // off the end already
-       if (lastBlock == no_blocks)
-               return QString();
-
        // c falls into a covered area, and we can guess which
        if (c >= unicode_blocks[lastBlock].start
            && c <= unicode_blocks[lastBlock].end)
@@ -177,8 +174,18 @@ QString getBlock(char_type c)
        int i = 0;
        while (i < no_blocks && c > unicode_blocks[i].end)
                ++i;
-       if (i == no_blocks || c < unicode_blocks[i].start)
+
+       if (i == no_blocks)
                return QString();
+
+       if (c < unicode_blocks[i].start) {
+               // 0 < i < no_blocks
+               // cache the previous block for guessing next time
+               lastBlock = i - 1;
+               return QString();
+       }
+
+       // 0 <= i < no_blocks
        // cache the last block for guessing next time
        lastBlock = i;
        return unicode_blocks[lastBlock].qname;