bc: make long-running dc drop data it does not need (when it can)

function                                             old     new   delta
zbc_vm_process                                       765     824     +59

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

diff --git a/miscutils/bc.c b/miscutils/bc.c
index bdee14de471472e1717cb645a9bfd3823f6d2d4a..7be2d0b9bb38b0975195167222848930ad368321 100644 (file)
--- a/miscutils/bc.c
+++ b/miscutils/bc.c
@@ -3437,11 +3437,11 @@ static BC_STATUS zdc_lex_token(BcLex *l)
 //                     break;
                case '\n':
                        // '\n' is BC_LEX_NLINE, not BC_LEX_WHITESPACE
-                       // (and "case '\n'" is not just empty here)
+                       // (and "case '\n':" is not just empty here)
                        // only to allow interactive dc have a way to exit
                        // "parse" stage of "parse,execute" loop
-                       // on '\n', not on _next_ token (which would mean
-                       // command are not executed on pressing <enter>).
+                       // on <enter>, not on _next_ token (which would mean
+                       // commands are not executed on pressing <enter>).
                        // IOW: typing "1p<enter>" should print "1" _at once_,
                        // not after some more input.
                        l->t.t = BC_LEX_NLINE;
@@ -6673,6 +6673,9 @@ static BC_STATUS zbc_vm_process(const char *text)
        if (s) RETURN_STATUS(s);
 
        while (G.prs.l.t.t != BC_LEX_EOF) {
+               BcInstPtr *ip;
+               BcFunc *f;
+
                dbg_lex("%s:%d G.prs.l.t.t:%d, parsing...", __func__, __LINE__, G.prs.l.t.t);
                if (IS_BC) {
 // FIXME: "eating" of stmt delimiters is coded inconsistently
@@ -6695,6 +6698,15 @@ static BC_STATUS zbc_vm_process(const char *text)
                        bc_program_reset();
                        break;
                }
+
+               ip = (void*)G.prog.exestack.v;
+#if SANITY_CHECKS
+               if (G.prog.exestack.len != 1) // should have only main's IP
+                       bb_error_msg_and_die("BUG:call stack");
+               if (ip->func != BC_PROG_MAIN)
+                       bb_error_msg_and_die("BUG:not MAIN");
+#endif
+               f = bc_program_func_BC_PROG_MAIN();
                // bc discards strings, constants and code after each
                // top-level statement in the "main program".
                // This prevents "yes 1 | bc" from growing its memory
@@ -6706,22 +6718,10 @@ static BC_STATUS zbc_vm_process(const char *text)
                // but bc stores function strings/constants in per-function
                // storage.
                if (IS_BC) {
-                       BcFunc *f;
-                       BcInstPtr *ip = (void*)G.prog.exestack.v;
-
 #if SANITY_CHECKS
                        if (G.prog.results.len != 0) // should be empty
                                bb_error_msg_and_die("BUG:data stack");
-                       if (G.prog.exestack.len != 1) // should have only main's IP
-                               bb_error_msg_and_die("BUG:call stack");
-                       if (ip->func != BC_PROG_MAIN)
-                               bb_error_msg_and_die("BUG:not MAIN");
 #endif
-//bb_error_msg("ip->func:%d >idx:%d >len:%d", ip->func, ip->inst_idx, ip->len);
-                       f = bc_program_func_BC_PROG_MAIN();
-//bb_error_msg("MAIN->code.len:%d >strs.len:%d >consts.len:%d", f->code.len, f->strs.len, f->consts.len); // labels, autos, nparams
-                       bc_vec_pop_all(&f->code);
-                       ip->inst_idx = 0;
                        IF_BC(bc_vec_pop_all(&f->strs);)
                        IF_BC(bc_vec_pop_all(&f->consts);)
                } else {
@@ -6731,7 +6731,26 @@ static BC_STATUS zbc_vm_process(const char *text)
                                s = zbc_lex_next(&G.prs.l);
                                if (s) RETURN_STATUS(s);
                        }
+
+                       if (G.prog.results.len == 0
+                        && G.prog.vars.len == 0
+                       ) {
+                               // If stack is empty and no registers exist (TODO: or they are all empty),
+                               // we can get rid of accumulated strings and constants.
+                               // In this example dc process should not grow
+                               // its memory consumption with time:
+                               // yes 1pc | dc
+                               IF_DC(bc_vec_pop_all(&G.prog.strs);)
+                               IF_DC(bc_vec_pop_all(&G.prog.consts);)
+                       }
+                       // The code is discarded always (below), thus this example
+                       // should also not grow its memory consumption with time,
+                       // even though its data stack is not empty:
+                       // { echo 1; yes dk; } | dc
                }
+               // We drop generated and executed code for both bc and dc:
+               bc_vec_pop_all(&f->code);
+               ip->inst_idx = 0;
        }
 
        dbg_lex_done("%s:%d done", __func__, __LINE__);