MIPS中的浮点寄存器数

Question

$f0, $f1 and so on are floating point registers in MIPS. There are 32 of them. How about the machines with 32 registers only? Where are the other registers like $s0 and $t0?

Answer 1

MIPS architecture has different set of registers:

• General purpose registers (numbered 0 to 31)
• Floating point registers (16 double precision registers)
• Some special registers (program counter PC (not architecturally visible), LO and HI registers to hold result of multiplication and division)

General purpose registers also have synonyms:

• $1 is named $at
• $2-$3 are named $v0 and $v1
• $4-$7 are named $a0-$a3
• $8-$15 are named $t0-$t7
• $16-$23 are named $s0-$s7
• $24-$25 are named $t0 and $t1
• $26-$27 are named $k0, $k1
• $28 is $gp (global pointer)
• $29 is $sp (stack pointer)
• $30 is $fp (frame pointer, not to be confused with floating point register)
• $31 is $ra (return address)

Also note that $0 is hardwired to constant zero

You have to see in each instruction which register set can be used (eg floating point operations will use floating point register set).