static unsigned int PerformComparison(const unsigned int opcode) { FPA11 *fpa11 = GET_FPA11(); unsigned int Fn, Fm; floatx80 rFn, rFm; int e_flag = opcode & 0x400000; /* 1 if CxFE */ int n_flag = opcode & 0x200000; /* 1 if CNxx */ unsigned int flags = 0; //printk("PerformComparison(0x%08x)\n",opcode); Fn = getFn(opcode); Fm = getFm(opcode); /* Check for unordered condition and convert all operands to 80-bit format. ?? Might be some mileage in avoiding this conversion if possible. Eg, if both operands are 32-bit, detect this and do a 32-bit comparison (cheaper than an 80-bit one). */ switch (fpa11->fType[Fn]) { case typeSingle: //printk("single.\n"); if (float32_is_nan(fpa11->fpreg[Fn].fSingle)) goto unordered; rFn = float32_to_floatx80(fpa11->fpreg[Fn].fSingle, &fpa11->fp_status); break; case typeDouble: //printk("double.\n"); if (float64_is_nan(fpa11->fpreg[Fn].fDouble)) goto unordered; rFn = float64_to_floatx80(fpa11->fpreg[Fn].fDouble, &fpa11->fp_status); break; case typeExtended: //printk("extended.\n"); if (floatx80_is_nan(fpa11->fpreg[Fn].fExtended)) goto unordered; rFn = fpa11->fpreg[Fn].fExtended; break; default: return 0; } if (CONSTANT_FM(opcode)) { //printk("Fm is a constant: #%d.\n",Fm); rFm = getExtendedConstant(Fm); if (floatx80_is_nan(rFm)) goto unordered; } else { //printk("Fm = r%d which contains a ",Fm); switch (fpa11->fType[Fm]) { case typeSingle: //printk("single.\n"); if (float32_is_nan(fpa11->fpreg[Fm].fSingle)) goto unordered; rFm = float32_to_floatx80(fpa11->fpreg[Fm].fSingle, &fpa11->fp_status); break; case typeDouble: //printk("double.\n"); if (float64_is_nan(fpa11->fpreg[Fm].fDouble)) goto unordered; rFm = float64_to_floatx80(fpa11->fpreg[Fm].fDouble, &fpa11->fp_status); break; case typeExtended: //printk("extended.\n"); if (floatx80_is_nan(fpa11->fpreg[Fm].fExtended)) goto unordered; rFm = fpa11->fpreg[Fm].fExtended; break; default: return 0; } } if (n_flag) { rFm.high ^= 0x8000; } return PerformComparisonOperation(rFn,rFm); unordered: /* ?? The FPA data sheet is pretty vague about this, in particular about whether the non-E comparisons can ever raise exceptions. This implementation is based on a combination of what it says in the data sheet, observation of how the Acorn emulator actually behaves (and how programs expect it to) and guesswork. */ flags |= CC_OVERFLOW; flags &= ~(CC_ZERO | CC_NEGATIVE); if (BIT_AC & readFPSR()) flags |= CC_CARRY; if (e_flag) float_raise(float_flag_invalid, &fpa11->fp_status); writeConditionCodes(flags); return 1; }