[reactos] 01/01: [USER32] Rewrite CharPrev(Ex)A functions and fix tests (#4860)

[Stanislav Motylkov]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=51f78918dab21a9e10468…

commit 51f78918dab21a9e10468ac02144e30cf4bccbb2
Author:     Stanislav Motylkov <x86corez(a)gmail.com>
AuthorDate: Tue Nov 8 00:42:26 2022 +0300
Commit:     Stanislav Motylkov <x86corez(a)gmail.com>
CommitDate: Sun Nov 13 13:22:26 2022 +0300

    [USER32] Rewrite CharPrev(Ex)A functions and fix tests (#4860)
    
    Fixes 48 failing tests of user32:CharFuncs.
    Only 12 minor failing tests are left!
    
    Thanks to Simone Mario Lombardo for the problem analysis!
    
    CORE-18415 CORE-18452
---
 win32ss/user/user32/windows/text.c | 41 ++++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 10 deletions(-)

diff --git a/win32ss/user/user32/windows/text.c b/win32ss/user/user32/windows/text.c
index bf730d749c9..1a73d674101 100644
--- a/win32ss/user/user32/windows/text.c
+++ b/win32ss/user/user32/windows/text.c
@@ -148,13 +148,25 @@ LPSTR
 WINAPI
 CharPrevA(LPCSTR start, LPCSTR ptr)
 {
-    while (*start && (start < ptr))
+    if (ptr > start)
     {
-        LPCSTR next = CharNextA(start);
-        if (next >= ptr) break;
-        start = next;
+        --ptr;
+        if (gpsi->dwSRVIFlags & SRVINFO_DBCSENABLED)
+        {
+            LPCSTR ch;
+            BOOL dbl = FALSE;
+
+            for (ch = ptr - 1; ch >= start; --ch)
+            {
+                if (!IsDBCSLeadByte(*ch))
+                    break;
+
+                dbl = !dbl;
+            }
+            if (dbl) --ptr;
+        }
     }
-    return (LPSTR)start;
+    return (LPSTR)ptr;
 }
 
 /*
@@ -164,13 +176,22 @@ LPSTR
 WINAPI
 CharPrevExA(WORD codepage, LPCSTR start, LPCSTR ptr, DWORD flags)
 {
-    while (*start && (start < ptr))
+    if (ptr > start)
     {
-        LPCSTR next = CharNextExA(codepage, start, flags);
-        if (next >= ptr) break;
-        start = next;
+        LPCSTR ch;
+        BOOL dbl = FALSE;
+
+        --ptr;
+        for (ch = ptr - 1; ch >= start; --ch)
+        {
+            if (!IsDBCSLeadByteEx(codepage, *ch))
+                break;
+
+            dbl = !dbl;
+        }
+        if (dbl) --ptr;
     }
-    return (LPSTR)start;
+    return (LPSTR)ptr;
 }
 
 /*