github.com/vc42/parquet-go@v0.0.0-20240320194221-1a9adb5f23f5/internal/bitpack/unpack_int64_purego.go (about)

     1  //go:build purego || !amd64
     2  
     3  package bitpack
     4  
     5  import "github.com/vc42/parquet-go/internal/unsafecast"
     6  
     7  func unpackInt64(dst []int64, src []byte, bitWidth uint) {
     8  	bits := unsafecast.BytesToUint32(src)
     9  	bitMask := uint64(1<<bitWidth) - 1
    10  	bitOffset := uint(0)
    11  
    12  	for n := range dst {
    13  		i := bitOffset / 32
    14  		j := bitOffset % 32
    15  		d := (uint64(bits[i]) & (bitMask << j)) >> j
    16  		if j+bitWidth > 32 {
    17  			k := 32 - j
    18  			d |= (uint64(bits[i+1]) & (bitMask >> k)) << k
    19  			if j+bitWidth > 64 {
    20  				k := 64 - j
    21  				d |= (uint64(bits[i+2]) & (bitMask >> k)) << k
    22  			}
    23  		}
    24  		dst[n] = int64(d)
    25  		bitOffset += bitWidth
    26  	}
    27  }