x87 set of registers

The x87 family does not use a directly addressable register set such as the main registers of the x86 processors; instead the x87 registers form a 8-level deep stack structure ranging from st0 to st7, where st0 is the top. 
x87 is a floating point-related subset (originally an extension) of the x86 architecture instruction set.

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gdb dump.

st0            0        (raw 0x00000000000000000000)
st1            0        (raw 0x00000000000000000000)
st2            1000000  (raw 0x4012f424000000000000)
st3            6        (raw 0x4001c000000000000000)
st4            736255   (raw 0x4012b3bff00000000000)
st5            -66.666666666666671403618238400667906    (raw 0xc0058555555555555800)
st6            736264   (raw 0x4012b3c0800000000000)
st7            736275   (raw 0x4012b3c1300000000000)