【RISC-V】fclass数值类型对照表

加强洁西卡2026-05-14 11:46

指令：

复制代码

vfclass.v vd, vs2, vm # Vector-vector

解析：

cpp 复制代码

if (vl > vlmax(e32, mf2)) vl = __riscv_vsetvl_e32mf2(vl);
vuint32mf2_t res;
for (size_t i = 0; i < vl; i++) {
  uint32_t t = 0;
  float32_t a = op1[i];
  bool sub = is_subnormal(op1[i]); // false for ±0
  if (a == -∞)     t |= 1<<0; //负无穷 ==   1 == 0x001
  if (a<0 && !sub) t |= 1<<1; //负正规数 ==   2 == 0x002; false for ±0.0
  if (a<0 &&  sub) t |= 1<<2; //负非正规数（指数） ==   4 == 0x004; false for ±0.0
  if (a === -0.0)  t |= 1<<3; //负零 ==   8 == 0x008
  if (a === +0.0)  t |= 1<<4; //正零 ==  16 == 0x010
  if (a>0 &&  sub) t |= 1<<5; //正非正规数 ==  32 == 0x020
  if (a>0 && !sub) t |= 1<<6; //正正规数 ==  64 == 0x040
  if (a == +∞)     t |= 1<<7; //正无穷 == 128 == 0x080
  if (isSNaN(a))   t |= 1<<8; //信号 == 256 == 0x100
  if (isQNaN(a))   t |= 1<<9; //静默 == 512 == 0x200
  res[i] = t;
}
for (size_t i = vl; i < vlmax; i++) res[i] = anything();
return res;

对应表格

代码逻辑判断 (伪代码)	分类名称	对应位	返回值 (十进制)	返回值 (十六进制)
`a == -∞`	负无穷 (Negative Infinity)	Bit 0	1	0x001
`a < 0 && !sub` (负数且非非正规数)	负正规数 (Negative Normal)	Bit 1	2	0x002
`a < 0 && sub` (负数且为非正规数)	负非正规数 (Negative Subnormal)	Bit 2	4	0x004
`a === -0.0`	负零 (Negative Zero)	Bit 3	8	0x008
`a === +0.0`	正零 (Positive Zero)	Bit 4	16	0x010
`a > 0 && sub` (正数且为非正规数)	正非正规数 (Positive Subnormal)	Bit 5	32	0x020
`a > 0 && !sub` (正数且非非正规数)	正正规数 (Positive Normal)	Bit 6	64	0x040
`a == +∞`	正无穷 (Positive Infinity)	Bit 7	128	0x080
`isSNaN(a)`	信号型 NaN (Signaling NaN)	Bit 8	256	0x100
`isQNaN(a)`	静默型 NaN (Quiet NaN)	Bit 9	512	0x200

举例：

cpp 复制代码

const float32_t vec1[DATALEN] = { 16.0, 16.50, -16.5000, -16.5001, +0.0, -0.0, -1e-38, 1e-38 };

结果：

cpp 复制代码

res[8] = {64, 64, 2, 2, 16, 8, 4, 32}