ARM base instruction -- csneg

Conditional Select Negation returns, in the destination register, the value of the first source register if the condition is TRUE, and otherwise returns the negated value of the second source register.

如果条件为TRUE，则条件选择否定在目标寄存器中返回第一个源寄存器的值，否则返回第二个源寄存器被否定的值。

32-bit variant
    Applies when sf == 0.
    CSNEG <Wd>, <Wn>, <Wm>, <cond>

64-bit variant
    Applies when sf == 1.
    CSNEG <Xd>, <Xn>, <Xm>, <cond>

Decode for all variants of this encoding
 integer d = UInt(Rd);
 integer n = UInt(Rn);
 integer m = UInt(Rm);
 integer datasize = if sf == '1' then 64 else 32;

Operation
 bits(datasize) result;
 bits(datasize) operand1 = X[n];
 bits(datasize) operand2 = X[m];
 
 if ConditionHolds(cond) then
     result = operand1;
 else
     result = NOT(operand2);
     result = result + 1;
 
 X[d] = result;

  415b90:    7100001f     cmp    w0, #0x0
  415b94:    1100fc01     add    w1, w0, #0x3f
  415b98:    1a80b021     csel    w1, w1, w0, lt  // lt = tstop
  415b9c:    6b0003e2     negs    w2, w0
  415ba0:    12001404     and    w4, w0, #0x3f
  415ba4:    12001442     and    w2, w2, #0x3f
  415ba8:    5a824482     csneg    w2, w4, w2, mi  // mi = first