bc: change bc_read_line() and zbc_vm_stdin() to avoid double buffers

function                                             old     new   delta
bc_read_line                                         129     124      -5
bc_vm_run                                            523     433     -90
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-95)             Total: -95 bytes
   text	   data	    bss	    dec	    hex	filename
 980445	    485	   7296	 988226	  f1442	busybox_old
 980350	    485	   7296	 988131	  f13e3	busybox_unstripped

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

1 files changed, 34 insertions, 27 deletions

diff --git a/miscutils/bc.c b/miscutils/bc.c
index bc2947161..7c4dfbb20 100644
--- a/miscutils/bc.c
+++ b/miscutils/bc.c
@@ -1226,6 +1226,7 @@ static void bc_vec_string(BcVec *v, size_t len, const char *str)
         bc_vec_pushZeroByte(v);
 }
 
+#if ENABLE_FEATURE_BC_SIGNALS && ENABLE_FEATURE_EDITING
 static void bc_vec_concat(BcVec *v, const char *str)
 {
         size_t len, slen;
@@ -1240,6 +1241,7 @@ static void bc_vec_concat(BcVec *v, const char *str)
 
         v->len = len;
 }
+#endif
 
 static void *bc_vec_item(const BcVec *v, size_t idx)
 {
@@ -1326,29 +1328,21 @@ static size_t bc_map_index(const BcVec *v, const void *ptr)
 }
 #endif
 
-static int push_input_byte(BcVec *vec, char c)
+static int bad_input_byte(char c)
 {
         if ((c < ' ' && c != '\t' && c != '\r' && c != '\n') // also allow '\v' '\f'?
          || c > 0x7e
         ) {
-                // Bad chars on this line, ignore entire line
                 bc_error_fmt("illegal character 0x%02x", c);
                 return 1;
         }
-        bc_vec_pushByte(vec, (char)c);
         return 0;
 }
 
+// Note: it _appends_ data from the stdin to vec.
 static void bc_read_line(BcVec *vec)
 {
-        bool bad_chars;
-
-        do {
-                int c;
-
-                bad_chars = 0;
-                bc_vec_pop_all(vec);
-
+ again:
                 fflush_and_check();
 
 #if ENABLE_FEATURE_BC_SIGNALS
@@ -1359,6 +1353,7 @@ static void bc_read_line(BcVec *vec)
                         // GNU dc says "Interrupt!"
                         fputs("\ninterrupted execution\n", stderr);
                 }
+
 # if ENABLE_FEATURE_EDITING
                 if (G_ttyin) {
                         int n, i;
@@ -1371,15 +1366,20 @@ static void bc_read_line(BcVec *vec)
                         }
                         i = 0;
                         for (;;) {
-                                c = line_buf[i++];
+                                char c = line_buf[i++];
                                 if (!c) break;
-                                bad_chars |= push_input_byte(vec, c);
+                                if (bad_input_byte(c)) goto again;
                         }
+                        bc_vec_concat(vec, line_buf);
 #  undef line_buf
                 } else
 # endif
 #endif
                 {
+                        int c;
+                        bool bad_chars = 0;
+                        size_t len = vec->len;
+
                         IF_FEATURE_BC_SIGNALS(errno = 0;)
                         do {
                                 c = fgetc(stdin);
@@ -1399,10 +1399,15 @@ static void bc_read_line(BcVec *vec)
                                         // printf 'print 123' | bc   - fails (syntax error)
                                         break;
                                 }
-                                bad_chars |= push_input_byte(vec, c);
+                                bad_chars |= bad_input_byte(c);
+                                bc_vec_pushByte(vec, (char)c);
                         } while (c != '\n');
+                        if (bad_chars) {
+                                // Bad chars on this line, ignore entire line
+                                vec->len = len;
+                                goto again;
+                        }
                 }
-        } while (bad_chars);
 
         bc_vec_pushZeroByte(vec);
 }
@@ -5374,12 +5379,12 @@ static BC_STATUS zbc_program_read(void)
 
         f = bc_program_func(BC_PROG_READ);
         bc_vec_pop_all(&f->code);
-        bc_char_vec_init(&buf);
 
         sv_file = G.prog.file;
         G.prog.file = NULL;
         G.in_read = 1;
 
+        bc_char_vec_init(&buf);
         bc_read_line(&buf);
 
         bc_parse_create(&parse, BC_PROG_READ);
@@ -7039,7 +7044,7 @@ err:
 static BC_STATUS zbc_vm_stdin(void)
 {
         BcStatus s;
-        BcVec buf, buffer;
+        BcVec buffer;
         size_t str;
         bool comment;
 
@@ -7047,8 +7052,6 @@ static BC_STATUS zbc_vm_stdin(void)
         bc_lex_file(&G.prs.l);
 
         bc_char_vec_init(&buffer);
-        bc_char_vec_init(&buf);
-        bc_vec_pushZeroByte(&buffer);
 
         // This loop is complex because the vm tries not to send any lines that end
         // with a backslash to the parser. The reason for that is because the parser
@@ -7058,16 +7061,18 @@ static BC_STATUS zbc_vm_stdin(void)
         comment = false;
         str = 0;
         for (;;) {
+                size_t prevlen = buffer.len;
                 char *string;
 
-                bc_read_line(&buf);
-                if (buf.len <= 1) // "" buf means EOF
+                bc_read_line(&buffer);
+                // No more input means EOF
+                if (buffer.len <= prevlen + 1) // (we expect +1 for NUL byte)
                         break;
 
-                string = buf.v;
+                string = buffer.v + prevlen;
                 while (*string) {
                         char c = *string;
-                        if (string == buf.v || string[-1] != '\\') {
+                        if (string == buffer.v || string[-1] != '\\') {
                                 // checking applet type is cheaper than accessing sbgn/send
                                 if (IS_BC) // bc: sbgn = send = '"'
                                         str ^= (c == '"');
@@ -7089,17 +7094,20 @@ static BC_STATUS zbc_vm_stdin(void)
                                 string++;
                         }
                 }
-                bc_vec_concat(&buffer, buf.v);
-                if (str || comment)
+                if (str || comment) {
+                        buffer.len--; // backstep over the trailing NUL byte
                         continue;
+                }
 
                 // Check for backslash+newline.
                 // we do not check that last char is '\n' -
                 // if it is not, then it's EOF, and looping back
                 // to bc_read_line() will detect it:
                 string -= 2;
-                if (string >= buf.v && *string == '\\')
+                if (string >= buffer.v && *string == '\\') {
+                        buffer.len--;
                         continue;
+                }
 
                 s = zbc_vm_process(buffer.v);
                 if (s) {
@@ -7121,7 +7129,6 @@ static BC_STATUS zbc_vm_stdin(void)
                 s = bc_error("comment end could not be found");
         }
 
-        bc_vec_free(&buf);
         bc_vec_free(&buffer);
         RETURN_STATUS(s);
 }