Why is vsldoi's SHB parameter signed?

[Gustavo Serra Scalet]

Hi,

I noticed that vsldoi instruction parameter SHB is being checked as a signed argument of 4 bits:

assembler_ppc.inline.hpp:804:inline void Assembler::vsldoi(  VectorRegister d, VectorRegister a, VectorRegister b, int si4)         { emit_int32( VSLDOI_OPCODE| vrt(d) | vra(a) | vrb(b) | vsldoi_shb(simm(si4,4))); }

I wonder why it was not defined as an unsigned parameter of 4 bits as described by ISA (attached). Is there a different way to look at it?!

Thanks
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