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DDA: don't bit-shift move_c. 

Next babystep, tiny enhancement: 8 bytes less binary size.
This commit is contained in:
Markus Hitter 2014-07-15 18:49:15 +02:00
parent b9c38051cc
commit e098a96bac
1 changed files with 6 additions and 5 deletions
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11
dda.c
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@ -866,19 +866,20 @@ void dda_clock() {
} }
if (recalc_speed) { if (recalc_speed) {
if (dda->n == 0) if (dda->n == 0)
move_c = pgm_read_dword(&c0_P[dda->fast_axis]) << 8; move_c = pgm_read_dword(&c0_P[dda->fast_axis]);
else else
// Explicit formula: c0 * (sqrt(n + 1) - sqrt(n)), // Explicit formula: c0 * (sqrt(n + 1) - sqrt(n)),
// approximation here: c0 * (1 / (2 * sqrt(n))). // approximation here: c0 * (1 / (2 * sqrt(n))).
// This >> 13 looks odd, but is verified with the explicit formula.
move_c = (pgm_read_dword(&c0_P[dda->fast_axis]) * move_c = (pgm_read_dword(&c0_P[dda->fast_axis]) *
int_inv_sqrt(dda->n)) >> 5; int_inv_sqrt(dda->n)) >> 13;
// TODO: most likely this whole check is obsolete. It was left as a // TODO: most likely this whole check is obsolete. It was left as a
// safety margin, only. Rampup steps calculation should be accurate // safety margin, only. Rampup steps calculation should be accurate
// now and give the requested target speed within a few percent. // now and give the requested target speed within a few percent.
if (move_c < (dda->c_min << 8)) { if (move_c < dda->c_min) {
// We hit max speed not always exactly. // We hit max speed not always exactly.
move_c = (dda->c_min << 8); move_c = dda->c_min;
// This is a hack which deals with movements with an unknown number of // This is a hack which deals with movements with an unknown number of
// acceleration steps. dda_create() sets a very high number, then, // acceleration steps. dda_create() sets a very high number, then,
@ -892,7 +893,7 @@ void dda_clock() {
// Write results. // Write results.
ATOMIC_START ATOMIC_START
dda->c = move_c; dda->c = (move_c << 8);
ATOMIC_END ATOMIC_END
} }
#endif #endif