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scrolling: optimize row access by assuming number of rows is a power of 2

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With this assumption, we can replace 'a % b' with 'a & (b - 1)'. In
terms of instructions, this means a fast 'and' instead of a slow
'div'.

Further optimize scrolling by:

* not double-initializing empty rows. Previously, grid_row_alloc()
  called calloc(), which was then followed by a memset() when
  scrolling. This is of course unnecessary.

* Don't loop the entire set of visible rows (this was done to ensure
  all visible rows had been allocated, and to prefetch the cell
  contents).

  This isn't necessary; only newly pulled in rows can be NULL. For
  now, don't prefetch at all.
This commit is contained in:
Daniel Eklöf 2019-08-22 17:33:23 +02:00
parent f0663c951e
commit 7c7720a3ab
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GPG key ID: 5BBD4992C116573F
5 changed files with 107 additions and 56 deletions
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17
render.c
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@ -568,8 +568,8 @@ grid_render(struct terminal *term)
* could be hidden. Or it could have been scrolled out of view.
*/
bool cursor_is_visible = false;
int view_end = (term->grid->view + term->rows - 1) % term->grid->num_rows;
int cursor_row = (term->grid->offset + term->cursor.row) % term->grid->num_rows;
int view_end = (term->grid->view + term->rows - 1) & (term->grid->num_rows - 1);
int cursor_row = (term->grid->offset + term->cursor.row) & (term->grid->num_rows - 1);
if (view_end >= term->grid->view) {
/* Not wrapped */
if (cursor_row >= term->grid->view && cursor_row <= view_end)
@ -595,8 +595,7 @@ grid_render(struct terminal *term)
/* Remember cursor coordinates so that we can erase it next
* time. Note that we need to re-align it against the view. */
int view_aligned_row
= (cursor_row - term->grid->view + term->grid->num_rows)
% term->grid->num_rows;
= (cursor_row - term->grid->view + term->grid->num_rows) & (term->grid->num_rows - 1);
term->render.last_cursor.actual = term->cursor;
term->render.last_cursor.in_view = (struct coord) {
@ -680,7 +679,7 @@ reflow(struct row **new_grid, int new_cols, int new_rows,
continue;
if (new_grid[r] == NULL)
new_grid[r] = grid_row_alloc(new_cols);
new_grid[r] = grid_row_alloc(new_cols, false);
struct cell *new_cells = new_grid[r]->cells;
const struct cell *old_cells = old_grid[r]->cells;
@ -730,8 +729,8 @@ render_resize(struct terminal *term, int width, int height)
const int new_cols = term->width / term->cell_width;
const int new_rows = term->height / term->cell_height;
const int new_normal_grid_rows = new_rows + scrollback_lines;
const int new_alt_grid_rows = new_rows;
const int new_normal_grid_rows = 1 << (32 - __builtin_clz(new_rows + scrollback_lines - 1));
const int new_alt_grid_rows = 1 << (32 - __builtin_clz(new_rows));
term->normal.offset %= new_normal_grid_rows;
term->normal.view %= new_normal_grid_rows;
@ -742,12 +741,12 @@ render_resize(struct terminal *term, int width, int height)
/* Allocate new 'normal' grid */
struct row **normal = calloc(new_normal_grid_rows, sizeof(normal[0]));
for (int r = 0; r < new_rows; r++)
normal[(term->normal.view + r) % new_normal_grid_rows] = grid_row_alloc(new_cols);
normal[(term->normal.view + r) & (new_normal_grid_rows - 1)] = grid_row_alloc(new_cols, true);;
/* Allocate new 'alt' grid */
struct row **alt = calloc(new_alt_grid_rows, sizeof(alt[0]));
for (int r = 0; r < new_rows; r++)
alt[(term->alt.view + r) % new_alt_grid_rows] = grid_row_alloc(new_cols);
alt[(term->alt.view + r) & (new_alt_grid_rows - 1)] = grid_row_alloc(new_cols, true);
/* Reflow content */
reflow(normal, new_cols, new_normal_grid_rows,