telnet: speed up processing of network input

function                                             old     new   delta
telnet_main                                         1482    1492     +10

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 43 insertions, 40 deletions

diff --git a/networking/telnet.c b/networking/telnet.c
index 7f65ff3e6..0ee65c532 100644
--- a/networking/telnet.c
+++ b/networking/telnet.c
@@ -94,19 +94,19 @@ enum {
         IACBUFSIZE  = 128,
 
         CHM_TRY = 0,
-        CHM_ON = 1,
+        CHM_ON  = 1,
         CHM_OFF = 2,
 
         UF_ECHO = 0x01,
-        UF_SGA = 0x02,
+        UF_SGA  = 0x02,
 
         TS_NORMAL = 0,
         TS_COPY = 1,
-        TS_IAC = 2,
-        TS_OPT = 3,
+        TS_IAC  = 2,
+        TS_OPT  = 3,
         TS_SUB1 = 4,
         TS_SUB2 = 5,
-        TS_CR = 6,
+        TS_CR   = 6,
 };
 
 typedef unsigned char byte;
@@ -244,25 +244,34 @@ static void handle_net_output(int len)
 
 static void handle_net_input(int len)
 {
+        byte c;
         int i;
-        int cstart = 0;
-
-        for (i = 0; i < len; i++) {
-                byte c = G.buf[i];
-
-                if (G.telstate == TS_NORMAL) { /* most typical state */
-                        if (c == IAC) {
-                                cstart = i;
-                                G.telstate = TS_IAC;
-                        }
-                        else if (c == '\r') {
-                                cstart = i + 1;
-                                G.telstate = TS_CR;
-                        }
-                        /* No IACs were seen so far, no need to copy
-                         * bytes within G.buf: */
-                        continue;
+        int cstart;
+
+        i = 0;
+        //bb_error_msg("[%u,'%.*s']", G.telstate, len, G.buf);
+        if (G.telstate == TS_NORMAL) { /* most typical state */
+                while (i < len) {
+                        c = G.buf[i];
+                        i++;
+                        if (c == IAC) /* unlikely */
+                                goto got_IAC;
+                        if (c != '\r') /* likely */
+                                continue;
+                        G.telstate = TS_CR;
+                        cstart = i;
+                        goto got_special;
                 }
+                full_write(STDOUT_FILENO, G.buf, len);
+                return;
+ got_IAC:
+                G.telstate = TS_IAC;
+                cstart = i - 1;
+ got_special: ;
+        }
+
+        for (; i < len; i++) {
+                c = G.buf[i];
 
                 switch (G.telstate) {
                 case TS_CR:
@@ -278,20 +287,19 @@ static void handle_net_input(int len)
                         /* Similar to NORMAL, but in TS_COPY we need to copy bytes */
                         if (c == IAC)
                                 G.telstate = TS_IAC;
-                        else
+                        else {
                                 G.buf[cstart++] = c;
-                        if (c == '\r')
-                                G.telstate = TS_CR;
+                                if (c == '\r')
+                                        G.telstate = TS_CR;
+                        }
                         break;
 
                 case TS_IAC: /* Prev char was IAC */
-                        if (c == IAC) { /* IAC IAC -> one IAC */
+                        switch (c) {
+                        case IAC: /* IAC IAC -> one IAC */
                                 G.buf[cstart++] = c;
                                 G.telstate = TS_COPY;
                                 break;
-                        }
-                        /* else */
-                        switch (c) {
                         case SB:
                                 G.telstate = TS_SUB1;
                                 break;
@@ -320,17 +328,12 @@ static void handle_net_input(int len)
                 }
         }
 
-        if (G.telstate != TS_NORMAL) {
-                /* We had some IACs, or CR */
-                if (G.iaclen)
-                        iac_flush();
-                if (G.telstate == TS_COPY) /* we aren't in the middle of IAC */
-                        G.telstate = TS_NORMAL;
-                len = cstart;
-        }
-
-        if (len)
-                full_write(STDOUT_FILENO, G.buf, len);
+        /* We had some IACs, or CR */
+        iac_flush();
+        if (G.telstate == TS_COPY) /* we aren't in the middle of IAC */
+                G.telstate = TS_NORMAL;
+        if (cstart != 0)
+                full_write(STDOUT_FILENO, G.buf, cstart);
 }
 
 static void put_iac(int c)