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![]() For VFP short vectors, the VFP registers are divided into a series of banks: for single-precision these are s0-s7, s8-s15, s16-s23 and s24-s31; for double-precision they are d0-d3, d4-d7, ... d28-d31. Some banks are "scalar" meaning that use of a register within them triggers a pure-scalar or mixed vector-scalar operation rather than a full vector operation. The scalar banks are s0-s7, d0-d3 and d16-d19. When using a bank as part of a vector operation, we iterate through it, increasing the register number by the specified stride each time, and wrapping around to the beginning of the bank. Unfortunately our calculation of the "increment" part of this was incorrect: vd = ((vd + delta_d) & (bank_mask - 1)) | (vd & bank_mask) will only do the intended thing if bank_mask has exactly one set high bit. For instance for doubles (bank_mask = 0xc), if we start with vd = 6 and delta_d = 2 then vd is updated to 12 rather than the intended 4. This only causes problems in the unlikely case that the starting register is not the first in its bank: if the register number doesn't have to wrap around then the expression happens to give the right answer. Fix this bug by abstracting out the "check whether register is in a scalar bank" and "advance register within bank" operations to utility functions which use the right bit masking operations. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> |
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