NASM 2.05 based x86 Instruction Reference[ch088]
A.5.68 FADD, FADDP: Floating-Point Addition FADD mem32 ; D8 /0 [8086,FPU] FADD mem64 ; DC /0 [8086,FPU] FADD fpureg ; D8 C0+r [8086,FPU] FADD ST0,fpureg ; D8 C0+r [8086,FPU] FADD TO fpureg ; DC C0+r [8086,FPU] FADD fpureg,ST0 ; DC C0+r [8086,FPU] FADDP fpureg ; DE C0+r [8086,FPU] FADDP fpureg,ST0 ; DE C0+r [8086,FPU] - FADD, given one operand, adds the operand to ST0 and stores the result back in ST0. If the operand has the TO modifier, the result is stored in the register given rather than in ST0. - FADDP performs the same function as FADD TO, but pops the register stack after storing the result. The given two-operand forms are synonyms for the one-operand forms. To add an integer value to ST0, use the FIADD instruction (section A.5.80).