Snapping four days of losses, the Sensex at the Bombay Stock Exchange jumped 285 points, or 1.6 percent, to 17,731, today, on renewed buying by funds, amid rising Asian markets, and easing crude oil prices. The 30-share Sensex had dropped more than 970 points in the past four trading sessions. The Nifty at the National Stock Exchange gained 94 points, or 1.8 percent, to 5,376.Stock markets in Japan, China, Hong Kong, Singapore and South Korea added between 0.2 percent and 1.7 percent.