1. A method, comprising: receiving a symbol that has been modulated with multiple bits in accordance with a signal constellation comprising multiple constellation points; computing a soft metric for a given bit in the received symbol by: finding a first constellation point that is closest to the received symbol in accordance with a distance measure; identifying a row or column of the constellation points that is closest to the first constellation point in accordance with the distance measure, and over which a value of the given bit is constant and is opposite to the value of the given bit in the first constellation point; searching over at least the identified row or column for a second constellation point that is closest to the received symbol in accordance with the distance measure; and calculating the soft metric based on the first and second constellation points; and reconstructing the value of the given bit in the received symbol based on the soft metric.