// +build amd64,!appengine

// func Ctz(x uint64) uint64
TEXT ·Ctz(SB),4,$0-16
        BSFQ  x+0(FP), AX
        JZ zero
        MOVQ AX, ret+8(FP)
        RET
zero:
        MOVQ $64, ret+8(FP)
        RET