> -/*
> - * This array maps current and lux.
> - *
> - * Ambient light sensing range is 3 to 55000 lux.
> - *
> - * This mapping is based on the following formula.
> - * illuminance = 10 ^ (current / 10)
> - */
> -static const struct gp2ap002_illuminance gp2ap002_illuminance_table[] = {
> - { .curr = 5, .lux = 3 },
> - { .curr = 6, .lux = 4 },
> - { .curr = 7, .lux = 5 },
> - { .curr = 8, .lux = 6 },
> - { .curr = 9, .lux = 8 },
> - { .curr = 10, .lux = 10 },
> - { .curr = 11, .lux = 12 },
> - { .curr = 12, .lux = 16 },
> - { .curr = 13, .lux = 20 },
> - { .curr = 14, .lux = 25 },
> - { .curr = 15, .lux = 32 },
> - { .curr = 16, .lux = 40 },
> - { .curr = 17, .lux = 50 },
> - { .curr = 18, .lux = 63 },
> - { .curr = 19, .lux = 79 },
> - { .curr = 20, .lux = 100 },
> - { .curr = 21, .lux = 126 },
> - { .curr = 22, .lux = 158 },
> - { .curr = 23, .lux = 200 },
> - { .curr = 24, .lux = 251 },
> - { .curr = 25, .lux = 316 },
> - { .curr = 26, .lux = 398 },
> - { .curr = 27, .lux = 501 },
> - { .curr = 28, .lux = 631 },
> - { .curr = 29, .lux = 794 },
> - { .curr = 30, .lux = 1000 },
> - { .curr = 31, .lux = 1259 },
> - { .curr = 32, .lux = 1585 },
> - { .curr = 33, .lux = 1995 },
> - { .curr = 34, .lux = 2512 },
> - { .curr = 35, .lux = 3162 },
> - { .curr = 36, .lux = 3981 },
> - { .curr = 37, .lux = 5012 },
> - { .curr = 38, .lux = 6310 },
> - { .curr = 39, .lux = 7943 },
> - { .curr = 40, .lux = 10000 },
> - { .curr = 41, .lux = 12589 },
> - { .curr = 42, .lux = 15849 },
> - { .curr = 43, .lux = 19953 },
> - { .curr = 44, .lux = 25119 },
> - { .curr = 45, .lux = 31623 },
> - { .curr = 46, .lux = 39811 },
> - { .curr = 47, .lux = 50119 },
> -};
...
> - for (i = 0; i < ARRAY_SIZE(gp2ap002_illuminance_table) - 1; i++) {
> - ill1 = &gp2ap002_illuminance_table[i];
> - ill2 = &gp2ap002_illuminance_table[i + 1];
> -
> - if (res > ill2->curr)
> - continue;
> - if ((res <= ill1->curr) && (res >= ill2->curr))
> - break;
That seems like a really, really contrived way to do a table lookup.
According to the table above, all successive input values between 5 and 47 are
covered, so shouldn't this be simple array indexing?
Something like:
#define gp2ap002_value_min 5
#define gp2ap002_value_max 47
static const unsigned int gp2ap002_value_to_illuminance_table[] = {
3, 4, 5, 6, 8, ...... 39811, 50119
};
#define gp2ap002_table_size ARRAY_SIZE(gp2ap002_value_to_illuminance_table)
if (res < gp2ap002_value_min)
return gp2ap002_value_to_illuminance_table[0];
if (res > gp2ap002_value_max)
return gp2ap002_value_to_illuminance_table[gp2ap002_table_size - 1];
lux = gp2ap002_value_to_illuminance_table[res - gp2ap002_value_min];
And since res is linear, interpolation won't even be needed.
What am I missing?
> + lux = int_pow(10, (res/10));
> + if (lux > INT_MAX) {
> + dev_err(gp2ap002->dev, "lux overflow, capped\n");
> + lux = INT_MAX;
> }
This is certainly better, but I wonder if it's worth the computational cost.
Also: It looks like int_pow doesn't saturate, so even though it uses 64bit
integer math, it might be better to move the range check before the calculation.
