collect_bits()

constexpr uint32_t collect_bits(uint32_t bm, ...)

From the value specified in the parameter bm, this function extracts the values corresponding to the 0..31 bit positions specified by the subsequent variadic parameters. The extracted values are arranged in the order of the parameters and returned as a bitmap.

The bit ordering of the resulting bitmap places the first parameter in the highest bit and the last parameter at bit 0.

uint32_t b1 = 0x12; // (b00010010)
uint32_t b2 = collect_bits(b1, 4, 2, 1, 0);
  // bit4->1, bit2->0, bit1->1, bit0->0
  // b2=0x10 (b1010)

In this example, bits 4, 2, 1, and 0 of b1 are extracted, resulting in (1,0,1,0). This is interpreted as b1010, resulting in a calculated value of 0x10.

Background

This function simplifies code where values are referenced or set in various bitmaps, such as IO port (DI, DO) statuses.