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怎么理解复数乘法指令cmpyr1 ?

l l5
Prodigy 30 points


代码里有_cmpyr1(c, 0x80000000), 从实际结果看, c实部/虚部都乘上了-1.

0x8000为什么是-1呢,  Q15的话, -1应该是0xffff吧?

和cmpyr有什么区别呢? cmpyr小1/2 ?

  • 0
    TI__Mastermind 27075 points

    最高位是符号位，15位数据。

  • 0 回复 Allen35065
    TI__Mastermind 27075 points

    见CPU and instruction set reference guide的描述

    cmpyr1

    sat((lsb16(src1) × msb16(src2)) + (msb16(src1) × lsb16(src2))) → tmp_e
    msb16(sat((tmp_e + 00004000h) << 1)) → lsb16(dst)
    sat((msb16(src1) × msb16(src2)) - (lsb16(src1) × lsb16(src2))) → tmp_o
    msb16(sat((tmp_e + 00004000h) << 1)) → msb16(dst)

    cmpyr

    sat((lsb16(src1) × msb16(src2)) + (msb16(src1) × lsb16(src2))) → tmp_e
    msb16(sat(tmp_e + 00008000h)) → lsb16(dst)
    sat((msb16(src1) × msb16(src2)) - (lsb16(src1) × lsb16(src2))) → tmp_o
    msb16(sat(tmp_o + 00008000h)) → msb16(dst)

  • 0 回复 Allen35065
    Prodigy 30 points

    以c=0x00010002, IQ实部虚部是(1,2). 

    _cmpyr1(0x00010002, 0x80000000)为例，

    cmpyr1

    sat((lsb16(src1) × msb16(src2)) + (msb16(src1) × lsb16(src2))) → tmp_e  :  0x10000
    msb16(sat((tmp_e + 00004000h) << 1)) → lsb16(dst) :  0x0002
    sat((msb16(src1) × msb16(src2)) - (lsb16(src1) × lsb16(src2))) → tmp_o : 0x8000
    msb16(sat((tmp_e + 00004000h) << 1)) → msb16(dst) : 0x0001

    这样结果没变啊?但我从内部打印上看，结果应该变成(-1,-2)