reverse_bits

Live Demo

The reverse_bits function returns the value with its bits in reversed order. Bit 0 becomes bit 31, bit 1 becomes bit 30, and so on.

Signature

bwsl

reverse_bits :: (int x) -> int {...}
reverse_bits :: (uint x) -> uint {...}

Parameters

Parameter	Type	Description
`x`	`int` or `uint`	The value to reverse

Return Value

Returns x with bits in reversed order.

Example

bwsl

pipeline BitReversedFFT {
  pass "Main" {
    compute "Main" [64, 1, 1] {
    // Bit-reversal permutation for FFT
    uint index = input.global_id.x;
    uint reversedIndex = reverse_bits(index) >> (32 - logN);

    // Swap elements at index and reversedIndex
    if (index < reversedIndex) {
        float2 temp = data[index];
        data[index] = data[reversedIndex];
        data[reversedIndex] = temp;
    }
    }
  }
}

Common Use Cases

FFT Bit Reversal

bwsl

// Bit-reversed addressing for FFT
uint bitRev = reverse_bits(i) >> (32 - log2N);
float2 sample = inputBuffer[bitRev];

Texture Coordinate Tricks

bwsl

// Create interesting patterns via bit manipulation
uint bits = uint(uv.x * 256.0);
uint reversed = reverse_bits(bits) >> 24;
float pattern = float(reversed) / 256.0;

Hash Functions

bwsl

// Part of hash function
uint hash = value;
hash = reverse_bits(hash);
hash ^= hash >> 16;

Fractal Patterns

bwsl

// Van der Corput sequence
uint bits = reverse_bits(sampleIndex);
float radical = float(bits) / float(0xFFFFFFFF);

Data Encoding

bwsl

// Reverse bits for specific protocols
uint encoded = reverse_bits(data);

Shift After Reverse

When working with values smaller than 32 bits, shift right after reversing. For an N-bit value: reverse_bits(x) >> (32 - N).

Van der Corput

Bit reversal is used to generate low-discrepancy sequences for quasi-Monte Carlo sampling.

Compiled Output

When compiled to GLSL:

glsl

bitfieldReverse(x)

When compiled to HLSL:

hlsl

reversebits(x)

When compiled to Metal:

metal

reverse_bits(x)

When compiled to SPIR-V:

Uses OpBitReverse instruction.

Test reverse_bits in a live shader

Live Demo

Signature

Parameters

Return Value

Example

Common Use Cases

FFT Bit Reversal

Texture Coordinate Tricks

Hash Functions

Fractal Patterns

Data Encoding

Compiled Output

See Also