Floating-point Convert precision (scalar). This instruction converts the floating-point value in the SIMD&FP source register to the precision for the destination register data type using the rounding mode that is determined by the FPCR and writes the result to the SIMD&FP destination register.
浮点转换精度（标量）。此指令使用FPCR确定的舍入模式将SIMD&FP源寄存器中的浮点值转换为目标寄存器数据类型的精度，并将结果写入SIMD&FPP目标寄存器。
Half-precision to single-precision variant
Applies when type == 11 && opc == 00.
FCVT <Sd>, <Hn>
Half-precision to double-precision variant
Applies when type == 11 && opc == 01.
FCVT <Dd>, <Hn>
Single-precision to half-precision variant
Applies when type == 00 && opc == 11.
FCVT <Hd>, <Sn>
Single-precision to double-precision variant
Applies when type == 00 && opc == 01.
FCVT <Dd>, <Sn>
Double-precision to half-precision variant
Applies when type == 01 && opc == 11.
FCVT <Hd>, <Dn>
Double-precision to single-precision variant
Applies when type == 01 && opc == 00.
FCVT <Sd>, <Dn>
int main()
{
char s[16];
int a;
float f;
strcpy(&s[0], "Hello, xiaozhi!");
a = 0x666;
f = 6.6;
printf("%s %x %f.\n", &s[0], a, f);
}
/*
Hello, xiaozhi! 666 6.600000.
*/
#if 0
/*
* arm
*/
000000000040055c <main>:
40055c: a9bd7bfd stp x29, x30, [sp, #-48]!
400560: 910003fd mov x29, sp // x29=fp=sp
400564: 910063a2 add x2, x29, #0x18 // x2=x29+0x18
400568: 90000000 adrp x0, 400000 <_init-0x3e8> // x0=400000
40056c: 9119a000 add x0, x0, #0x668 // x0=400668
400570: a9400400 ldp x0, x1, [x0] // x0=[x0], x1=[x0+8]
400574: a9000440 stp x0, x1, [x2] // [x2]=x0, [x2+8]=x1
400578: 5280ccc0 mov w0, #0x666 // #1638 w0=0x666
40057c: b9002fa0 str w0, [x29, #44] // x29+44=w0
400580: 52866660 mov w0, #0x3333 // #13107 w0=0x3333
400584: 72a81a60 movk w0, #0x40d3, lsl #16 // w0=0x40d3<<16
400588: 1e270000 fmov s0, w0 // s0=w0
40058c: bd002ba0 str s0, [x29, #40] // x29+40=s0
400590: bd402ba0 ldr s0, [x29, #40] // s0=x29+40
400594: 1e22c000 fcvt d0, s0 // d0=s0
400598: 910063a1 add x1, x29, #0x18 // x1=x29+0x18
40059c: 90000000 adrp x0, 400000 <_init-0x3e8>
4005a0: 9119e000 add x0, x0, #0x678
4005a4: b9402fa2 ldr w2, [x29, #44] // w2=x29+44
4005a8: 97ffffaa bl 400450 <printf@plt> // printf()
4005ac: 52800000 mov w0, #0x0 // #0
4005b0: a8c37bfd ldp x29, x30, [sp], #48
4005b4: d65f03c0 ret
#endif