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VarAction2: Detect and replace scaled reads of train/RV/ship current speed

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This commit is contained in:
Jonathan G Rennison
2022-05-26 21:31:20 +01:00
parent 730b84e262
commit 2360b3e93e
4 changed files with 27 additions and 3 deletions
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19
src/newgrf.cpp
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@@ -5929,10 +5929,25 @@ static void NewSpriteGroup(ByteReader *buf)
break;
case DSGA_OP_SDIV:
if ((prev_inference & VA2AIF_SIGNED_NON_NEGATIVE) && adjust.variable == 0x1A && adjust.shift_num == 0 && HasExactlyOneBit(adjust.and_mask)) {
uint shift_count = FindFirstBit(adjust.and_mask);
if (group->adjusts.size() >= 3 && shift_count == 16 && varsize == 4 && (feature == GSF_TRAINS || feature == GSF_ROADVEHICLES || feature == GSF_SHIPS)) {
const DeterministicSpriteGroupAdjust &prev = group->adjusts[group->adjusts.size() - 2];
DeterministicSpriteGroupAdjust &prev2 = group->adjusts[group->adjusts.size() - 3];
if (prev.operation == DSGA_OP_MUL && prev.type == DSGA_TYPE_NONE && prev.variable == 0x1A && prev.shift_num == 0 && prev.and_mask <= 0xFFFF &&
(prev2.operation == DSGA_OP_RST || group->adjusts.size() == 3) && prev2.type == DSGA_TYPE_NONE && prev2.variable == 0xB4 && prev2.shift_num == 0 && prev2.and_mask == 0xFFFF) {
/* Replace with scaled current speed */
prev2.variable = A2VRI_VEHICLE_CURRENT_SPEED_SCALED;
prev2.parameter = prev.and_mask;
group->adjusts.pop_back();
group->adjusts.pop_back();
inference = VA2AIF_SIGNED_NON_NEGATIVE;
break;
}
}
/* Convert to a shift */
adjust.operation = DSGA_OP_SHR;
adjust.and_mask = FindFirstBit(adjust.and_mask);
inference |= VA2AIF_SIGNED_NON_NEGATIVE;
adjust.and_mask = shift_count;
inference = VA2AIF_SIGNED_NON_NEGATIVE;
}
default:
break;