We present SoftExplorer, a tool to estimate and analyze the power and energy consumption of an algorithm from the C program. The consumption of every loop is analyzed, and the in influence of the data mapping is characterized. Several models of processor are available, from the simple RISC ARM7 to the very complex VLIW DSP TI-C67. Cache misses, pipeline stalls, and internal / external memory accesses are taken into account. We show how to analyze and optimize the power and energy consumption, and how to choose a processor and its operating frequency, for a MPEG-1 decoder. We also explain how to find the best data mapping for a DSP application.