From 654d1e675a3dc1f598aeadb0824bdb3357820a59 Mon Sep 17 00:00:00 2001 From: Andreas Sandberg Date: Mon, 30 Sep 2013 12:00:20 +0200 Subject: x86: Add support for loading 32-bit and 80-bit floats in the x87 The x87 FPU supports three floating point formats: 32-bit, 64-bit, and 80-bit floats. The current gem5 implementation supports 32-bit and 64-bit floats, but only works correctly for 64-bit floats. This changeset fixes the 32-bit float handling by correctly loading and rounding (using truncation) 32-bit floats instead of simply truncating the bit pattern. 80-bit floats are loaded by first loading the 80-bits of the float to two temporary integer registers. A micro-op (cvtint_fp80) then converts the contents of the two integer registers to the internal FP representation (double). Similarly, when storing an 80-bit float, there are two conversion routines (ctvfp80h_int and cvtfp80l_int) that convert an internal FP register to 80-bit and stores the upper 64-bits or lower 32-bits to an integer register, which is the written to memory using normal integer stores. --- src/arch/x86/isa/microops/fpop.isa | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) (limited to 'src/arch/x86/isa/microops/fpop.isa') diff --git a/src/arch/x86/isa/microops/fpop.isa b/src/arch/x86/isa/microops/fpop.isa index 8a77914d9..3c6753712 100644 --- a/src/arch/x86/isa/microops/fpop.isa +++ b/src/arch/x86/isa/microops/fpop.isa @@ -295,9 +295,10 @@ let {{ class ConvOp(FpBinaryOp): abstract = True op_class = 'FloatCvtOp' - def __init__(self, dest, src1): + def __init__(self, dest, src1, **kwargs): super(ConvOp, self).__init__(dest, src1, \ - "InstRegIndex(FLOATREG_MICROFP0)") + "InstRegIndex(FLOATREG_MICROFP0)", \ + **kwargs) # These probably shouldn't look at the ExtMachInst directly to figure # out what size to use and should instead delegate that to the macroop's @@ -324,6 +325,34 @@ let {{ SDestReg = merge(SDestReg, intSrcReg1, 4); ''' + # Convert two integers registers representing an 80-bit floating + # point number to an x87 register. + class cvtint_fp80(FpBinaryOp): + code = ''' + uint8_t bits[10]; + *(uint64_t *)(bits + 0) = SSrcReg1; + *(uint16_t *)(bits + 8) = (uint16_t)SSrcReg2; + FpDestReg = loadFloat80(bits); + ''' + + # Convert an x87 register (double) into extended precision and + # extract the highest 64 bits. + class cvtfp80h_int(ConvOp): + code = ''' + char bits[10]; + storeFloat80(bits, FpSrcReg1); + SDestReg = *(uint64_t *)(bits + 0); + ''' + + # Convert an x87 register (double) into extended precision and + # extract the lowest 16 bits. + class cvtfp80l_int(ConvOp): + code = ''' + char bits[10]; + storeFloat80(bits, FpSrcReg1); + SDestReg = *(uint16_t *)(bits + 8); + ''' + # These need to consider size at some point. They'll always use doubles # for the moment. class addfp(FpBinaryOp): -- cgit v1.2.3