Changeset 888c06e in mainline for kernel/genarch/src/fb/fb.c

Timestamp:

2025-04-17T16:13:24Z (5 days ago)

Author:

Jiří Zárevúcky <zarevucky.jiri@…>

Branches:

master

Children:

61c91532, eb2187c4

Parents:

c4cfe4c

Message:

Avoid using general division and modulo ops in framebuffer

These can be very expensive and slow on CPUs without a hardware
divider, and sometimes even on those that have it.

File:

• kernel/genarch/src/fb/fb.c (modified) (13 diffs)

kernel/genarch/src/fb/fb.c

@@ -81 +81 @@
         ((glyph) * (instance)->glyphbytes + (y) * (instance)->glyphscanline)
 
+#define TAB_WIDTH 8
+
 typedef void (*rgb_conv_t)(void *, uint32_t);
 
@@ -99 +101 @@
 
         /** Number of rows that fit on framebuffer */
-        unsigned int rowtrim;
+        unsigned int screen_rows;
 
         unsigned int scanline;
@@ -124 +126 @@
         /** Partial character between writes */
         mbstate_t mbstate;
+
+        unsigned int row;
+        unsigned int column;
 } fb_instance_t;
 
@@ -250 +255 @@
 
         unsigned int rel_row = row - instance->offset_row;
-        if (rel_row >= instance->rowtrim)
+        if (rel_row >= instance->screen_rows)
                 return;
 
@@ -262 +267 @@
 }
 
-/** Scroll screen down by one row
- *
- */
-static void screen_scroll(fb_instance_t *instance)
-{
-        if ((!instance->parea.mapped) || (console_override)) {
-                for (unsigned int rel_row = 0; rel_row < instance->rowtrim; rel_row++) {
-                        unsigned int y = ROW2Y(rel_row);
-                        unsigned int row = rel_row + instance->offset_row;
-
-                        for (unsigned int yd = 0; yd < FONT_SCANLINES; yd++) {
-                                unsigned int x;
-                                unsigned int col;
-                                size_t bb_pos = BB_POS(instance, 0, row);
-                                size_t bb_pos1 = BB_POS(instance, 0, row + 1);
-
-                                for (col = 0, x = 0; col < instance->cols;
-                                    col++, x += FONT_WIDTH) {
-                                        uint16_t glyph;
-
-                                        if (row < instance->rows - 1) {
-                                                if (instance->backbuf[bb_pos] ==
-                                                    instance->backbuf[bb_pos1])
-                                                        goto skip;
-
-                                                glyph = instance->backbuf[bb_pos1];
-                                        } else
-                                                glyph = 0;
-
-                                        memcpy(&instance->addr[FB_POS(instance, x, y + yd)],
-                                            &instance->glyphs[GLYPH_POS(instance, glyph, yd)],
-                                            instance->glyphscanline);
-                                skip:
-                                        BB_NEXT_COL(bb_pos);
-                                        BB_NEXT_COL(bb_pos1);
-                                }
-                        }
-                }
-        }
-
-        /*
-         * Implement backbuffer scrolling by wrapping around
-         * the cyclic buffer.
-         */
-
-        instance->start_row++;
-        if (instance->start_row == instance->rows)
-                instance->start_row = 0;
-
-        memsetw(&instance->backbuf[BB_POS(instance, 0, instance->rows - 1)],
-            instance->cols, 0);
-}
-
 static void cursor_put(fb_instance_t *instance)
 {
-        unsigned int col = instance->position % instance->cols;
-        unsigned int row = instance->position / instance->cols;
+        unsigned int col = instance->column;
+        unsigned int row = instance->row;
 
         glyph_draw(instance, fb_font_glyph(U_CURSOR), col, row, true);
@@ -325 +277 @@
 static void cursor_remove(fb_instance_t *instance)
 {
-        unsigned int col = instance->position % instance->cols;
-        unsigned int row = instance->position / instance->cols;
+        unsigned int col = instance->column;
+        unsigned int row = instance->row;
 
         glyph_draw(instance, instance->backbuf[BB_POS(instance, col, row)],
@@ -376 +328 @@
 static void fb_redraw_internal(fb_instance_t *instance)
 {
-        for (unsigned int rel_row = 0; rel_row < instance->rowtrim; rel_row++) {
+        for (unsigned int rel_row = 0; rel_row < instance->screen_rows; rel_row++) {
                 unsigned int y = ROW2Y(rel_row);
                 unsigned int row = rel_row + instance->offset_row;
@@ -407 +359 @@
         }
 
-        if (ROW2Y(instance->rowtrim) < instance->yres) {
+        if (ROW2Y(instance->screen_rows) < instance->yres) {
                 unsigned int y;
 
-                for (y = ROW2Y(instance->rowtrim); y < instance->yres; y++)
+                for (y = ROW2Y(instance->screen_rows); y < instance->yres; y++)
                         memcpy(&instance->addr[FB_POS(instance, 0, y)],
                             instance->bgscan, instance->bgscanbytes);
@@ -416 +368 @@
 }
 
+/** Scroll screen down by one row
+ *
+ */
+static void screen_scroll(fb_instance_t *instance)
+{
+        /*
+         * Implement backbuffer scrolling by wrapping around
+         * the cyclic buffer.
+         */
+
+        instance->start_row++;
+        if (instance->start_row == instance->rows)
+                instance->start_row = 0;
+
+        if ((!instance->parea.mapped) || (console_override)) {
+                fb_redraw_internal(instance);
+        }
+}
+
+static void _advance_row(fb_instance_t *instance)
+{
+        instance->column = 0;
+        instance->row++;
+}
+
+static void _advance_column(fb_instance_t *instance)
+{
+        instance->column++;
+        if (instance->column == instance->cols)
+                _advance_row(instance);
+}
+
 /** Print character to screen
  *
@@ -425 +409 @@
         switch (ch) {
         case '\n':
-                instance->position += instance->cols;
-                instance->position -= instance->position % instance->cols;
+                _advance_row(instance);
                 break;
         case '\r':
-                instance->position -= instance->position % instance->cols;
+                instance->column = 0;
                 break;
         case '\b':
-                if (instance->position % instance->cols)
-                        instance->position--;
+                if (instance->column > 0)
+                        instance->column--;
                 break;
         case '\t':
                 do {
                         glyph_draw(instance, fb_font_glyph(' '),
-                            instance->position % instance->cols,
-                            instance->position / instance->cols, false);
-                        instance->position++;
-                } while (((instance->position % instance->cols) % 8 != 0) &&
-                    (instance->position < instance->cols * instance->rows));
+                            instance->column,
+                            instance->row, false);
+                        _advance_column(instance);
+                } while (instance->column % TAB_WIDTH != 0);
                 break;
         default:
                 glyph_draw(instance, fb_font_glyph(ch),
-                    instance->position % instance->cols,
-                    instance->position / instance->cols, false);
-                instance->position++;
-        }
-
-        if (instance->position >= instance->cols * instance->rows) {
-                instance->position -= instance->cols;
+                    instance->column,
+                    instance->row, false);
+                _advance_column(instance);
+        }
+
+        while (instance->row >= instance->rows) {
+                instance->row--;
                 screen_scroll(instance);
         }
@@ -482 +464 @@
         spinlock_lock(&instance->lock);
 
-        if (instance->offset_row >= instance->rowtrim / 2)
-                instance->offset_row -= instance->rowtrim / 2;
+        if (instance->offset_row >= instance->screen_rows / 2)
+                instance->offset_row -= instance->screen_rows / 2;
         else
                 instance->offset_row = 0;
@@ -501 +483 @@
         spinlock_lock(&instance->lock);
 
-        if (instance->offset_row + instance->rowtrim / 2 <=
-            instance->rows - instance->rowtrim)
-                instance->offset_row += instance->rowtrim / 2;
+        if (instance->offset_row + instance->screen_rows / 2 <=
+            instance->rows - instance->screen_rows)
+                instance->offset_row += instance->screen_rows / 2;
         else
-                instance->offset_row = instance->rows - instance->rowtrim;
+                instance->offset_row = instance->rows - instance->screen_rows;
 
         fb_redraw_internal(instance);
@@ -624 +606 @@
         instance->scanline = props->scan;
 
-        instance->rowtrim = Y2ROW(instance->yres);
+        instance->screen_rows = Y2ROW(instance->yres);
 
         instance->cols = X2COL(instance->xres);
-        instance->rows = FB_PAGES * instance->rowtrim;
-
-        instance->start_row = instance->rows - instance->rowtrim;
+        instance->rows = FB_PAGES * instance->screen_rows;
+
+        instance->start_row = instance->rows - instance->screen_rows;
         instance->offset_row = instance->start_row;
-        instance->position = instance->start_row * instance->cols;
+        instance->row = instance->start_row;
+        instance->column = 0;
 
         instance->glyphscanline = FONT_WIDTH * instance->pixelbytes;