Multiplies two floating-point operands, adds the result to one floating-point operand, and places the negative of the result in a floating-point register.
PowerPC | |
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fnmadd | FRT,FRA,FRC,FRB |
fnmadd. | FRT,FRA,FRC,FRB |
POWER | |
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fnma | FRT,FRA,FRC,FRB |
fnma. | FRT,FRA,FRC,FRB |
PowerPC | |
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fnmadds | FRT,FRA,FRC,FRB |
fnmadds. | FRT,FRA,FRC,FRB |
The fnmadd and fnma instructions multiply the 64-bit, double-precision floating-point operand in floating-point register (FPR) FRA by the 64,bit, double-precision floating-point operand in FPR FRC, and add the 64-bit, double-precision floating-point operand in FPR FRB to the result of the multiplication.
The fnmadds instruction multiplies the 32-bit, single-precision floating-point operand in FPR FRA by the 32-bit, single-precision floating-point operand in FPR FRC, and adds the 32-bit, single-precision floating-point operand in FPR FRB to the result of the multiplication.
The result of the addition is rounded under control of the Floating-Point Rounding Control Field RN of the Floating-Point Status and Control Register.
Note: If an operand is a denormalized number, then it is prenormalized before the operation is begun.
The fnmadd and fnma instructions are identical to the fmadd and fma (Floating Multiply- Add Single) instructions with the final result negated, but with the following exceptions:
The Floating-Point Result Flags Field of the Floating-Point Status and Control Register is set to the class and sign of the result, except for Invalid Operation Exceptions, when the Floating-Point Invalid Operation Exception Enable bit is 1.
The fnmadd, fnmadds, and fnma instructions each have two syntax forms. Each syntax form has a different effect on Condition Register Field 1.
Syntax Form | Floating-Point Status and Control Register | Record Bit (Rc) | Condition Register Field 1 |
fnmadd | C,FL,FG,FE,FU,FR,FI,OX,UX, XX,VXSNAN,VXISI,VXIMZ | 0 | None |
fnmadd. | C,FL,FG,FE,FU,FR,FI,OX,UX, XX,VXSNAN,VXISI,VXIMZ | 1 | FX,FEX,VX,OX |
fnmadds | C,FL,FG,FE,FU,FR,FI,OX,UX, XX,VXSNAN,VXISI,VXIMZ | 0 | None |
fnmadds. | C,FL,FG,FE,FU,FR,FI,OX,UX, XX,VXSNAN,VXISI,VXIMZ | 1 | FX,FEX,VX,OX |
fnma | C,FL,FG,FE,FU,FR,FI,OX,UX, XX,VXSNAN,VXISI,VXIMZ | 0 | None |
fnma. | C,FL,FG,FE,FU,FR,FI,OX,UX, XX,VXSNAN,VXISI,VXIMZ | 1 | FX,FEX,VX,OX |
All syntax forms of the fnmadd, fnmadds, and fnma instructions always affect the Floating-Point Status and Control Register. If the syntax form sets the Record (Rc) bit to 1, the instruction affects the Floating-Point Exception (FX), Floating-Point Enabled Exception (FEX), Floating-Point Invalid Operation Exception (VX), and Floating-Point Overflow Exception (OX) bits in Condition Register Field 1.
Note: Rounding occurs before the result of the addition is negated. Depending on RN, an inexact value may result.
# Assume FPR 4 contains 0xC053 4000 0000 0000. # Assume FPR 5 contains 0x400C 0000 0000 0000. # Assume FPR 7 contains 0x3DE2 6AB4 B33c 110A. # Assume FPSCR = 0. fnmadd 6,4,5,7 # FPR 6 now contains 0x4070 D7FF FFFF F6CB. # FPSCR now contains 0x8206 4000.
# Assume FPR 4 contains 0xC053 4000 0000 0000. # Assume FPR 5 contains 0x400C 0000 0000 0000. # Assume FPR 7 contains 0x3DE2 6AB4 B33c 110A. # Assume FPSCR = 0 and CR = 0. fnmadd. 6,4,5,7 # FPR 6 now contains 0x4070 D7FF FFFF F6CB. # FPSCR now contains 0x8206 4000. # CR now contains 0x0800 0000.
Interpreting the Contents of a Floating-Point Register.