x86汇编，如何在C中重现fscale

Question

浮点数为31.0和0.85842 ...如何在C中重现以下fscale运算以获得与1843450267.9相同的结果？

(gdb) info float
  R7: Valid   0x3fff8000000000000000 +1
  R6: Valid   0x3fff8000000000000000 +1
  R5: Valid   0x4003f800000000000000 +31
=>R4: Valid   0x3ffedbc1a337fffff775 +0.8584234248846768147

(gdb) x/i $eip
0x11212 <xxx>:  fscale
(gdb) si
(gdb) info float
  R7: Valid   0x3fff8000000000000000 +1
  R6: Valid   0x3fff8000000000000000 +1
  R5: Valid   0x4003f800000000000000 +31
=>R4: Valid   0x401ddbc1a337fffff775 +1843450267.999999745