diff --git a/src/core/ngx_conf_file.c b/src/core/ngx_conf_file.c
index 9e4b30a..e06315e 100644
--- a/src/core/ngx_conf_file.c
+++ b/src/core/ngx_conf_file.c
@@ -883,10 +883,10 @@
 
     value = cf->args->elts;
 
-    if (ngx_strcasecmp(value[1].data, "on") == 0) {
+    if (ngx_strcasecmp(value[1].data, (u_char *) "on") == 0) {
         *fp = 1;
 
-    } else if (ngx_strcasecmp(value[1].data, "off") == 0) {
+    } else if (ngx_strcasecmp(value[1].data, (u_char *) "off") == 0) {
         *fp = 0;
 
     } else {
diff --git a/src/core/ngx_inet.c b/src/core/ngx_inet.c
index 09ff014..de4cae2 100644
--- a/src/core/ngx_inet.c
+++ b/src/core/ngx_inet.c
@@ -233,7 +233,7 @@
     len = u->url.len;
     p = u->url.data;
 
-    if (ngx_strncasecmp(p, "unix:", 5) == 0) {
+    if (ngx_strncasecmp(p, (u_char *) "unix:", 5) == 0) {
 
 #if (NGX_HAVE_UNIX_DOMAIN)
 
diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index e12edbd..fe8cfac 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -428,6 +428,68 @@
 }
 
 
+/*
+ * We use ngx_strcasecmp()/ngx_strncasecmp() for 7-bit ASCII string only,
+ * and implement our own ngx_strcasecmp()/ngx_strncasecmp()
+ * to avoid libc locale overhead.  Besides, we use the ngx_uint_t's
+ * instead of the u_char's, because they are slightly faster.
+ */
+
+ngx_int_t
+ngx_strcasecmp(u_char *s1, u_char *s2)
+{
+    ngx_uint_t  c1, c2;
+
+    for ( ;; ) {
+        c1 = (ngx_uint_t) *s1++;
+        c2 = (ngx_uint_t) *s2++;
+
+        c1  = (c1 >= 'A' && c1 <= 'Z') ? (c1 | 0x20) : c1;
+        c2  = (c2 >= 'A' && c2 <= 'Z') ? (c2 | 0x20) : c2;
+
+        if (c1 == c2) {
+
+            if (c1) {
+                continue;
+            }
+
+            return 0;
+        }
+
+        return c1 - c2;
+    }
+}
+
+
+ngx_int_t
+ngx_strncasecmp(u_char *s1, u_char *s2, size_t n)
+{
+    ngx_uint_t  c1, c2;
+
+    while (n) {
+        c1 = (ngx_uint_t) *s1++;
+        c2 = (ngx_uint_t) *s2++;
+
+        c1  = (c1 >= 'A' && c1 <= 'Z') ? (c1 | 0x20) : c1;
+        c2  = (c2 >= 'A' && c2 <= 'Z') ? (c2 | 0x20) : c2;
+
+        if (c1 == c2) {
+
+            if (c1) {
+                n--;
+                continue;
+            }
+
+            return 0;
+        }
+
+        return c1 - c2;
+    }
+
+    return 0;
+}
+
+
 ngx_int_t
 ngx_rstrncmp(u_char *s1, u_char *s2, size_t n)
 {
diff --git a/src/core/ngx_string.h b/src/core/ngx_string.h
index 6700639..1565000 100644
--- a/src/core/ngx_string.h
+++ b/src/core/ngx_string.h
@@ -24,29 +24,12 @@
 } ngx_keyval_t;
 
 
-#define ngx_string(str)  { sizeof(str) - 1, (u_char *) str }
-#define ngx_null_string  { 0, NULL }
+#define ngx_string(str)     { sizeof(str) - 1, (u_char *) str }
+#define ngx_null_string     { 0, NULL }
 
 
-#define ngx_tolower(c)     (u_char) ((c >= 'A' && c <= 'Z') ? (c | 0x20) : c)
-#define ngx_toupper(c)     (u_char) ((c >= 'a' && c <= 'z') ? (c & ~0x20) : c)
-
-
-#if (NGX_WIN32)
-
-#define ngx_strncasecmp(s1, s2, n)                                           \
-                           strnicmp((const char *) s1, (const char *) s2, n)
-#define ngx_strcasecmp(s1, s2)                                               \
-                           stricmp((const char *) s1, (const char *) s2)
-
-#else
-
-#define ngx_strncasecmp(s1, s2, n)                                           \
-                           strncasecmp((const char *) s1, (const char *) s2, n)
-#define ngx_strcasecmp(s1, s2)                                               \
-                           strcasecmp((const char *) s1, (const char *) s2)
-
-#endif
+#define ngx_tolower(c)      (u_char) ((c >= 'A' && c <= 'Z') ? (c | 0x20) : c)
+#define ngx_toupper(c)      (u_char) ((c >= 'a' && c <= 'z') ? (c & ~0x20) : c)
 
 
 #define ngx_strncmp(s1, s2, n)  strncmp((const char *) s1, (const char *) s2, n)
@@ -128,6 +111,9 @@
 u_char * ngx_cdecl ngx_snprintf(u_char *buf, size_t max, const char *fmt, ...);
 u_char *ngx_vsnprintf(u_char *buf, size_t max, const char *fmt, va_list args);
 
+ngx_int_t ngx_strcasecmp(u_char *s1, u_char *s2);
+ngx_int_t ngx_strncasecmp(u_char *s1, u_char *s2, size_t n);
+
 ngx_int_t ngx_rstrncmp(u_char *s1, u_char *s2, size_t n);
 ngx_int_t ngx_rstrncasecmp(u_char *s1, u_char *s2, size_t n);
 ngx_int_t ngx_memn2cmp(u_char *s1, u_char *s2, size_t n1, size_t n2);
diff --git a/src/http/modules/ngx_http_addition_filter_module.c b/src/http/modules/ngx_http_addition_filter_module.c
index 5025f56..9480082 100644
--- a/src/http/modules/ngx_http_addition_filter_module.c
+++ b/src/http/modules/ngx_http_addition_filter_module.c
@@ -100,8 +100,8 @@
         return ngx_http_next_header_filter(r);
     }
 
-    if (ngx_strncasecmp(r->headers_out.content_type.data, "text/html",
-                        sizeof("text/html") - 1)
+    if (ngx_strncasecmp(r->headers_out.content_type.data,
+                        (u_char *) "text/html", sizeof("text/html") - 1)
         != 0)
     {
         return ngx_http_next_header_filter(r);
diff --git a/src/http/modules/ngx_http_charset_filter_module.c b/src/http/modules/ngx_http_charset_filter_module.c
index cae9bbe..0139cc6 100644
--- a/src/http/modules/ngx_http_charset_filter_module.c
+++ b/src/http/modules/ngx_http_charset_filter_module.c
@@ -239,8 +239,10 @@
             } else {
                 ct = r->headers_out.content_type.data;
 
-                if (ngx_strncasecmp(ct, "text/", 5) != 0
-                    && ngx_strncasecmp(ct, "application/x-javascript", 24) != 0)
+                if (ngx_strncasecmp(ct, (u_char *) "text/", 5) != 0
+                    && ngx_strncasecmp(ct,
+                                      (u_char *) "application/x-javascript", 24)
+                       != 0)
                 {
                     return ngx_http_next_header_filter(r);
                 }
@@ -1118,7 +1120,7 @@
     table->src = src;
     table->dst = dst;
 
-    if (ngx_strcasecmp(value[2].data, "utf-8") == 0) {
+    if (ngx_strcasecmp(value[2].data, (u_char *) "utf-8") == 0) {
         table->src2dst = ngx_pcalloc(cf->pool, 256 * NGX_UTF_LEN);
         if (table->src2dst == NULL) {
             return NGX_CONF_ERROR;
@@ -1372,7 +1374,7 @@
     c->name = *name;
     c->length = 0;
 
-    if (ngx_strcasecmp(name->data, "utf-8") == 0) {
+    if (ngx_strcasecmp(name->data, (u_char *) "utf-8") == 0) {
         c->utf8 = 1;
 
     } else {
diff --git a/src/http/modules/ngx_http_headers_filter_module.c b/src/http/modules/ngx_http_headers_filter_module.c
index 8d17b43..599bd14 100644
--- a/src/http/modules/ngx_http_headers_filter_module.c
+++ b/src/http/modules/ngx_http_headers_filter_module.c
@@ -411,7 +411,7 @@
 
     value = cf->args->elts;
 
-    if (ngx_strcasecmp(value[1].data, "cache-control") == 0) {
+    if (ngx_strcasecmp(value[1].data, (u_char *) "cache-control") == 0) {
         hcf->cache_control = value[2];
         return NGX_CONF_OK;
     }
diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
index 63ee8fd..cbd2ce8 100644
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -2111,11 +2111,11 @@
 
     url = &value[1];
 
-    if (ngx_strncasecmp(url->data, "http://", 7) == 0) {
+    if (ngx_strncasecmp(url->data, (u_char *) "http://", 7) == 0) {
         add = 7;
         port = 80;
 
-    } else if (ngx_strncasecmp(url->data, "https://", 8) == 0) {
+    } else if (ngx_strncasecmp(url->data, (u_char *) "https://", 8) == 0) {
 
 #if (NGX_HTTP_SSL)
 
diff --git a/src/http/modules/ngx_http_range_filter_module.c b/src/http/modules/ngx_http_range_filter_module.c
index 0c945d8..62b537f 100644
--- a/src/http/modules/ngx_http_range_filter_module.c
+++ b/src/http/modules/ngx_http_range_filter_module.c
@@ -152,7 +152,9 @@
 
     if (r->headers_in.range == NULL
         || r->headers_in.range->value.len < 7
-        || ngx_strncasecmp(r->headers_in.range->value.data, "bytes=", 6) != 0)
+        || ngx_strncasecmp(r->headers_in.range->value.data,
+                           (u_char *) "bytes=", 6)
+           != 0)
     {
         r->headers_out.accept_ranges = ngx_list_push(&r->headers_out.headers);
         if (r->headers_out.accept_ranges == NULL) {
diff --git a/src/http/modules/ngx_http_referer_module.c b/src/http/modules/ngx_http_referer_module.c
index f3597a1..b2c2ef5 100644
--- a/src/http/modules/ngx_http_referer_module.c
+++ b/src/http/modules/ngx_http_referer_module.c
@@ -106,7 +106,7 @@
     ref = r->headers_in.referer->value.data;
 
     if (len < sizeof("http://i.ru") - 1
-        || (ngx_strncasecmp(ref, "http://", 7) != 0))
+        || (ngx_strncasecmp(ref, (u_char *) "http://", 7) != 0))
     {
         if (rlcf->blocked_referer) {
             goto valid;
diff --git a/src/http/modules/ngx_http_ssi_filter_module.c b/src/http/modules/ngx_http_ssi_filter_module.c
index c8e11bf..e1d0e92 100644
--- a/src/http/modules/ngx_http_ssi_filter_module.c
+++ b/src/http/modules/ngx_http_ssi_filter_module.c
@@ -1890,10 +1890,13 @@
             return NGX_HTTP_SSI_ERROR;
         }
 
-        if (wait->len == 2 && ngx_strncasecmp(wait->data, "no", 2) == 0) {
+        if (wait->len == 2
+            && ngx_strncasecmp(wait->data, (u_char *) "no", 2) == 0)
+        {
             wait = NULL;
 
-        } else if (wait->len != 3 || ngx_strncasecmp(wait->data, "yes", 3) != 0)
+        } else if (wait->len != 3
+                   || ngx_strncasecmp(wait->data, (u_char *) "yes", 3) != 0)
         {
             ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                           "invalid value \"%V\" in the \"wait\" parameter",
diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index c35ccac..0a686c3 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -12,7 +12,7 @@
 
 
 typedef struct {
-    char      *name;
+    u_char    *name;
     uint32_t   method;
 } ngx_http_method_name_t;
 
@@ -1247,7 +1247,9 @@
     encoded = r->headers_in.authorization->value;
 
     if (encoded.len < sizeof("Basic ") - 1
-        || ngx_strncasecmp(encoded.data, "Basic ", sizeof("Basic ") - 1) != 0)
+        || ngx_strncasecmp(encoded.data, (u_char *) "Basic ",
+                           sizeof("Basic ") - 1)
+           != 0)
     {
         r->headers_in.user.data = (u_char *) "";
         return NGX_DECLINED;
@@ -2681,19 +2683,19 @@
 
 
 static ngx_http_method_name_t  ngx_methods_names[] = {
-   { "GET",       (uint32_t) ~NGX_HTTP_GET },
-   { "HEAD",      (uint32_t) ~NGX_HTTP_HEAD },
-   { "POST",      (uint32_t) ~NGX_HTTP_POST },
-   { "PUT",       (uint32_t) ~NGX_HTTP_PUT },
-   { "DELETE",    (uint32_t) ~NGX_HTTP_DELETE },
-   { "MKCOL",     (uint32_t) ~NGX_HTTP_MKCOL },
-   { "COPY",      (uint32_t) ~NGX_HTTP_COPY },
-   { "MOVE",      (uint32_t) ~NGX_HTTP_MOVE },
-   { "OPTIONS",   (uint32_t) ~NGX_HTTP_OPTIONS },
-   { "PROPFIND" , (uint32_t) ~NGX_HTTP_PROPFIND },
-   { "PROPPATCH", (uint32_t) ~NGX_HTTP_PROPPATCH },
-   { "LOCK",      (uint32_t) ~NGX_HTTP_LOCK },
-   { "UNLOCK",    (uint32_t) ~NGX_HTTP_UNLOCK },
+   { (u_char *) "GET",       (uint32_t) ~NGX_HTTP_GET },
+   { (u_char *) "HEAD",      (uint32_t) ~NGX_HTTP_HEAD },
+   { (u_char *) "POST",      (uint32_t) ~NGX_HTTP_POST },
+   { (u_char *) "PUT",       (uint32_t) ~NGX_HTTP_PUT },
+   { (u_char *) "DELETE",    (uint32_t) ~NGX_HTTP_DELETE },
+   { (u_char *) "MKCOL",     (uint32_t) ~NGX_HTTP_MKCOL },
+   { (u_char *) "COPY",      (uint32_t) ~NGX_HTTP_COPY },
+   { (u_char *) "MOVE",      (uint32_t) ~NGX_HTTP_MOVE },
+   { (u_char *) "OPTIONS",   (uint32_t) ~NGX_HTTP_OPTIONS },
+   { (u_char *) "PROPFIND" , (uint32_t) ~NGX_HTTP_PROPFIND },
+   { (u_char *) "PROPPATCH", (uint32_t) ~NGX_HTTP_PROPPATCH },
+   { (u_char *) "LOCK",      (uint32_t) ~NGX_HTTP_LOCK },
+   { (u_char *) "UNLOCK",    (uint32_t) ~NGX_HTTP_UNLOCK },
    { NULL, 0 }
 };
 
diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index d37fead..b366f79 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -1285,14 +1285,16 @@
 
     if (r->headers_in.connection) {
         if (r->headers_in.connection->value.len == 5
-            && ngx_strcasecmp(r->headers_in.connection->value.data, "close")
+            && ngx_strcasecmp(r->headers_in.connection->value.data,
+                              (u_char *) "close")
                == 0)
         {
             r->headers_in.connection_type = NGX_HTTP_CONNECTION_CLOSE;
 
         } else if (r->headers_in.connection->value.len == 10
                    && ngx_strcasecmp(r->headers_in.connection->value.data,
-                                     "keep-alive") == 0)
+                                     (u_char *) "keep-alive")
+                      == 0)
         {
             r->headers_in.connection_type = NGX_HTTP_CONNECTION_KEEP_ALIVE;
 
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 5286000..79d372c 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2313,7 +2313,7 @@
 
         while (*++p == ' ') { /* void */ }
 
-        if (ngx_strncasecmp(p, "charset=", 8) != 0) {
+        if (ngx_strncasecmp(p, (u_char *) "charset=", 8) != 0) {
             continue;
         }
 
diff --git a/src/imap/ngx_imap_auth_http_module.c b/src/imap/ngx_imap_auth_http_module.c
index 668a952..f3e11e8 100644
--- a/src/imap/ngx_imap_auth_http_module.c
+++ b/src/imap/ngx_imap_auth_http_module.c
@@ -477,8 +477,10 @@
             len = ctx->header_name_end - ctx->header_name_start;
 
             if (len == sizeof("Auth-Status") - 1
-                && ngx_strncasecmp(ctx->header_name_start, "Auth-Status",
-                                   sizeof("Auth-Status") - 1) == 0)
+                && ngx_strncasecmp(ctx->header_name_start,
+                                   (u_char *) "Auth-Status",
+                                   sizeof("Auth-Status") - 1)
+                   == 0)
             {
                 len = ctx->header_end - ctx->header_start;
 
@@ -539,8 +541,10 @@
             }
 
             if (len == sizeof("Auth-Server") - 1
-                && ngx_strncasecmp(ctx->header_name_start, "Auth-Server",
-                                   sizeof("Auth-Server") - 1) == 0)
+                && ngx_strncasecmp(ctx->header_name_start,
+                                   (u_char *) "Auth-Server",
+                                   sizeof("Auth-Server") - 1)
+                    == 0)
             {
                 ctx->addr.len = ctx->header_end - ctx->header_start;
                 ctx->addr.data = ctx->header_start;
@@ -549,8 +553,10 @@
             }
 
             if (len == sizeof("Auth-Port") - 1
-                && ngx_strncasecmp(ctx->header_name_start, "Auth-Port",
-                                   sizeof("Auth-Port") - 1) == 0)
+                && ngx_strncasecmp(ctx->header_name_start,
+                                   (u_char *) "Auth-Port",
+                                   sizeof("Auth-Port") - 1)
+                   == 0)
             {
                 ctx->port.len = ctx->header_end - ctx->header_start;
                 ctx->port.data = ctx->header_start;
@@ -559,8 +565,10 @@
             }
 
             if (len == sizeof("Auth-User") - 1
-                && ngx_strncasecmp(ctx->header_name_start, "Auth-User",
-                                   sizeof("Auth-User") - 1) == 0)
+                && ngx_strncasecmp(ctx->header_name_start,
+                                   (u_char *) "Auth-User",
+                                   sizeof("Auth-User") - 1)
+                   == 0)
             {
                 s->login.len = ctx->header_end - ctx->header_start;
 
@@ -578,8 +586,10 @@
             }
 
             if (len == sizeof("Auth-Pass") - 1
-                && ngx_strncasecmp(ctx->header_name_start, "Auth-Pass",
-                                   sizeof("Auth-Pass") - 1) == 0)
+                && ngx_strncasecmp(ctx->header_name_start,
+                                   (u_char *) "Auth-Pass",
+                                   sizeof("Auth-Pass") - 1)
+                   == 0)
             {
                 s->passwd.len = ctx->header_end - ctx->header_start;
 
@@ -597,8 +607,10 @@
             }
 
             if (len == sizeof("Auth-Wait") - 1
-                && ngx_strncasecmp(ctx->header_name_start, "Auth-Wait",
-                                   sizeof("Auth-Wait") - 1) == 0)
+                && ngx_strncasecmp(ctx->header_name_start,
+                                   (u_char *) "Auth-Wait",
+                                   sizeof("Auth-Wait") - 1)
+                   == 0)
             {
                 n = ngx_atoi(ctx->header_start,
                              ctx->header_end - ctx->header_start);
diff --git a/src/imap/ngx_imap_handler.c b/src/imap/ngx_imap_handler.c
index 6ee6b33..db0b8ce 100644
--- a/src/imap/ngx_imap_handler.c
+++ b/src/imap/ngx_imap_handler.c
@@ -802,7 +802,9 @@
 
                 if (arg[0].len == 5) {
 
-                    if (ngx_strncasecmp(arg[0].data, "LOGIN", 5) == 0) {
+                    if (ngx_strncasecmp(arg[0].data, (u_char *) "LOGIN", 5)
+                        == 0)
+                    {
 
                         if (s->args.nelts != 1) {
                             rc = NGX_IMAP_PARSE_INVALID_COMMAND;
@@ -816,7 +818,10 @@
 
                         break;
 
-                    } else if (ngx_strncasecmp(arg[0].data, "PLAIN", 5) == 0) {
+                    } else if (ngx_strncasecmp(arg[0].data, (u_char *) "PLAIN",
+                                               5)
+                               == 0)
+                    {
 
                         if (s->args.nelts == 1) {
                             s->imap_state = ngx_pop3_auth_plain;
@@ -856,7 +861,9 @@
                     }
 
                 } else if (arg[0].len == 8
-                           && ngx_strncasecmp(arg[0].data, "CRAM-MD5", 8) == 0)
+                           && ngx_strncasecmp(arg[0].data,
+                                              (u_char *) "CRAM-MD5", 8)
+                              == 0)
                 {
                     s->imap_state = ngx_pop3_auth_cram_md5;