term: runtime switch between a ‘fast’ and a ‘generic’ ASCII print function

term_print() is called whenever the client application “prints”
something to the grid. It is called for both ASCII and UTF-8
characters, and needs to handle sixels, insert mode and ASCII
vs. graphical charsets.

Since it’s on the hot path, this becomes unnecessarily slow.

This patch adds a “fast” version of term_print(), tailored for the
common case: ASCII characters in non-insert mode, without any sixels
and non-graphical charsets.

A new function, term_update_ascii_printer(), has been added, and must
be called whenever:

* The currently selected charset *index* changes
* The currently selected charset changes (from ASCII to graphical, or
  vice verse)
* Sixels are added to the grid
* Sixels are removed from the grid
* Insert mode is enabled/disabled

csi.c

@@ -1136,6 +1136,7 @@ csi_dispatch(struct terminal *term, uint8_t final)
 
             case 4:   /* Insert Mode - IRM */
                 term->insert_mode = true;
+                term_update_ascii_printer(term);
                 break;
 
             case 12:  /* Send/receive Mode - SRM */
@@ -1156,6 +1157,7 @@ csi_dispatch(struct terminal *term, uint8_t final)
             switch (vt_param_get(term, 0, 0)) {
             case 4:   /* Insert Mode - IRM */
                 term->insert_mode = false;
+                term_update_ascii_printer(term);
                 break;
 
             case 2:   /* Keyboard Action Mode - AM */

sixel.c

@@ -331,6 +331,7 @@ sixel_scroll_up(struct terminal *term, int rows)
         }
     }
 
+    term_update_ascii_printer(term);
     verify_sixels(term);
 }
 
@@ -353,6 +354,7 @@ sixel_scroll_down(struct terminal *term, int rows)
             break;
     }
 
+    term_update_ascii_printer(term);
     verify_sixels(term);
 }
 
@@ -552,6 +554,8 @@ sixel_overwrite_by_rectangle(
         _sixel_overwrite_by_rectangle(term, 0, col, height - rows_to_wrap_around, width);
     } else
         _sixel_overwrite_by_rectangle(term, start, col, height, width);
+
+    term_update_ascii_printer(term);
 }
 
 /* Row numbers are relative to grid offset */
@@ -605,6 +609,8 @@ sixel_overwrite_by_row(struct terminal *term, int _row, int col, int width)
             }
         }
     }
+
+    term_update_ascii_printer(term);
 }
 
 void
@@ -859,6 +865,7 @@ sixel_unhook(struct terminal *term)
     LOG_DBG("you now have %zu sixels in current grid",
             tll_length(term->grid->sixel_images));
 
+    term_update_ascii_printer(term);
     render_refresh(term);
 }
 

terminal.c

@@ -1187,6 +1187,8 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
 #endif
     };
 
+   term_update_ascii_printer(term);
+
     for (size_t i = 0; i < 4; i++) {
         size_t j = 0;
         tll_foreach(conf->fonts[i], it) {
@@ -1702,6 +1704,8 @@ term_reset(struct terminal *term, bool hard)
     term_ime_enable(term);
 #endif
 
+    term_update_ascii_printer(term);
+
     if (!hard)
         return;
 
@@ -2335,6 +2339,7 @@ term_restore_cursor(struct terminal *term, const struct cursor *cursor)
 
     term->vt.attrs = term->vt.saved_attrs;
     term->charsets = term->saved_charsets;
+    term_update_ascii_printer(term);
 }
 
 void
@@ -2813,6 +2818,21 @@ term_print(struct terminal *term, wchar_t wc, int width)
 {
     xassert(width > 0);
 
+    if (unlikely(term->charsets.set[term->charsets.selected] == CHARSET_GRAPHIC) &&
+        wc >= 0x60 && wc <= 0x7e)
+    {
+        /* 0x60 - 0x7e */
+        static const wchar_t vt100_0[] = {
+            L'◆', L'▒', L'␉', L'␌', L'␍', L'␊', L'°', L'±', /* ` - g */
+            L'␤', L'␋', L'┘', L'┐', L'┌', L'└', L'┼', L'⎺', /* h - o */
+            L'⎻', L'─', L'⎼', L'⎽', L'├', L'┤', L'┴', L'┬', /* p - w */
+            L'│', L'≤', L'≥', L'π', L'≠', L'£', L'·',       /* x - ~ */
+        };
+
+        xassert(width == 1);
+        wc = vt100_0[wc - 0x60];
+    }
+
     print_linewrap(term);
     print_insert(term, width);
 
@@ -2855,6 +2875,50 @@ term_print(struct terminal *term, wchar_t wc, int width)
         xassert(!term->grid->cursor.lcf);
 }
 
+static void
+ascii_printer_generic(struct terminal *term, wchar_t wc)
+{
+    term_print(term, wc, 1);
+}
+
+static void
+ascii_printer_fast(struct terminal *term, wchar_t wc)
+{
+    xassert(term->charsets.set[term->charsets.selected] == CHARSET_ASCII);
+    xassert(!term->insert_mode);
+    xassert(tll_length(term->grid->sixel_images) == 0);
+
+    print_linewrap(term);
+
+    /* *Must* get current cell *after* linewrap+insert */
+    struct row *row = term->grid->cur_row;
+    struct cell *cell = &row->cells[term->grid->cursor.point.col];
+
+    cell->wc = term->vt.last_printed = wc;
+    cell->attrs = term->vt.attrs;
+
+    row->dirty = true;
+    cell->attrs.clean = 0;
+
+    /* Advance cursor */
+    if (unlikely(++term->grid->cursor.point.col >= term->cols)) {
+        term->grid->cursor.lcf = true;
+        term->grid->cursor.point.col--;
+    } else
+        xassert(!term->grid->cursor.lcf);
+}
+
+void
+term_update_ascii_printer(struct terminal *term)
+{
+    term->ascii_printer =
+        unlikely(tll_length(term->grid->sixel_images) > 0 ||
+                 term->charsets.set[term->charsets.selected] == CHARSET_GRAPHIC ||
+                 term->insert_mode)
+        ? &ascii_printer_generic
+        : &ascii_printer_fast;
+}
+
 enum term_surface
 term_surface_kind(const struct terminal *term, const struct wl_surface *surface)
 {

terminal.h

@@ -266,6 +266,8 @@ struct terminal {
     struct reaper *reaper;
     const struct config *conf;
 
+    void (*ascii_printer)(struct terminal *term, wchar_t c);
+
     pid_t slave;
     int ptmx;
 
@@ -607,6 +609,8 @@ struct terminal *term_init(
 bool term_shutdown(struct terminal *term);
 int term_destroy(struct terminal *term);
 
+void term_update_ascii_printer(struct terminal *term);
+
 void term_reset(struct terminal *term, bool hard);
 bool term_to_slave(struct terminal *term, const void *data, size_t len);
 bool term_paste_data_to_slave(

vt.c

@@ -184,11 +184,13 @@ action_execute(struct terminal *term, uint8_t c)
     case '\x0e':
         /* SO - shift out */
         term->charsets.selected = 1; /* G1 */
+        term_update_ascii_printer(term);
         break;
 
     case '\x0f':
         /* SI - shift in */
         term->charsets.selected = 0; /* G0 */
+        term_update_ascii_printer(term);
         break;
 
         /*
@@ -230,21 +232,7 @@ action_execute(struct terminal *term, uint8_t c)
 static void
 action_print(struct terminal *term, uint8_t c)
 {
-    /* 0x60 - 0x7e */
-    static const wchar_t vt100_0[] = {
-        L'◆', L'▒', L'␉', L'␌', L'␍', L'␊', L'°', L'±', /* ` - g */
-        L'␤', L'␋', L'┘', L'┐', L'┌', L'└', L'┼', L'⎺', /* h - o */
-        L'⎻', L'─', L'⎼', L'⎽', L'├', L'┤', L'┴', L'┬', /* p - w */
-        L'│', L'≤', L'≥', L'π', L'≠', L'£', L'·',       /* x - ~ */
-    };
-
-    if (unlikely(term->charsets.set[term->charsets.selected] == CHARSET_GRAPHIC) &&
-        c >= 0x60 && c <= 0x7e)
-    {
-        term_print(term, vt100_0[c - 0x60], 1);
-    } else {
-        term_print(term, c, 1);
-    }
+    term->ascii_printer(term, c);
 }
 
 static void
@@ -414,11 +402,13 @@ action_esc_dispatch(struct terminal *term, uint8_t final)
         case 'N':
             /* SS2 - Single Shift 2 */
             term->charsets.selected = 2; /* G2 */
+            term_update_ascii_printer(term);
             break;
 
         case 'O':
             /* SS3 - Single Shift 3 */
             term->charsets.selected = 3; /* G3 */
+            term_update_ascii_printer(term);
             break;
 
         case '\\':
@@ -453,6 +443,7 @@ action_esc_dispatch(struct terminal *term, uint8_t final)
                 '+' ? 3 : -1;
             xassert(idx != -1);
             term->charsets.set[idx] = CHARSET_GRAPHIC;
+            term_update_ascii_printer(term);
             break;
         }
 
@@ -465,7 +456,7 @@ action_esc_dispatch(struct terminal *term, uint8_t final)
                 '+' ? 3 : -1;
             xassert(idx != -1);
             term->charsets.set[idx] = CHARSET_ASCII;
-
+            term_update_ascii_printer(term);
             break;
         }
         }