A U.S. judge Tuesday sentenced a socially awkward math whiz-turned-futures trader who earned tens of millions of dollars over several years and helped trigger a U.S. stock market “flash crash” from his parents’ suburban London home to time served and a year’s home confinement, sparing him imprisonment after prosecutors praised his cooperation and said his crimes were entirely unmotivated by greed. Government prosecutors and defense lawyers described the 41-year-old Navinder Singh Sarao as autistic in memos filed before sentencing in Chicago federal court.