We present SoftExplorer, a tool to estimate the power and energy consumption of an algorithm directly from the C program. Four models of processor are available, from the simple RISC ARM7 to the very complex VLIW DSP TIC67. Important phenomena are taken into account, like cache misses, pipeline stalls, and internal / external memory accesses. We show how to use SoftExplorer to find the best data mapping for a DSP application, and to choose a processor and its operating frequency for a MPEG-1 decoder.