how to use the floating point hardware in nios II custom instructions

okey, i think the problem is the "hardware_fp_cust_inst_no_divider_present" option

if i uncheck it, the objdump file is

c=a*b;

1082c4: e0fffc17 ldw r3,-16(fp)

1082c8: e0bffd17 ldw r2,-12(fp)

1082cc: 1885ff32 custom 252,r2,r3,r2

1082d0: e0bffe15 stw r2,-8(fp)

c=ALT_CI_NIOS_CUSTOM_INSTR_FLOATING_POINT_0(0,b,a); //*

108324: e13ffd17 ldw r4,-12(fp)

108328: 01084000 call 108400 <__fixsfsi>

10832c: 1021883a mov r16,r2

108330: e13ffc17 ldw r4,-16(fp)

108334: 01084000 call 108400 <__fixsfsi>

108338: 8085ff32 custom 252,r2,r16,r2

10833c: 1009883a mov r4,r2

108340: 01084780 call 108478 <__floatsisf>

108344: 1007883a mov r3,r2

108348: e0fffe15 stw r3,-8(fp)

at this time, the system.h file is still "__builtin_custom_inii",

it leads to c=ALT_CI_NIOS_CUSTOM_INSTR_FLOATING_POINT_0(0,b,a); returns wrong value, like mikedsouze said .

but that is not important, because the c=a*b works.