| //===-- fnan2.c - Handle single-precision NaN inputs to binary operation --===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This helper function is available for use by single-precision float |
| // arithmetic implementations to handle propagating NaNs from the input |
| // operands to the output, in a way that matches Arm hardware FP. |
| // |
| // On input, a and b are floating-point numbers in IEEE 754 encoding, and at |
| // least one of them must be a NaN. The return value is the correct output NaN. |
| // |
| // A signalling NaN in the input (with bit 22 clear) takes priority over any |
| // quiet NaN, and is adjusted on return by setting bit 22 to make it quiet. If |
| // both inputs are the same type of NaN then the first input takes priority: |
| // the input a is used instead of b. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include <stdint.h> |
| |
| uint32_t __compiler_rt_fnan2(uint32_t a, uint32_t b) { |
| // Make shifted-left copies of a and b to discard the sign bit. Then add 1 at |
| // the bit position where the quiet vs signalling bit ended up. This squashes |
| // all the signalling NaNs to the top of the range of 32-bit values, from |
| // 0xff800001 to 0xffffffff inclusive; meanwhile, all the quiet NaN values |
| // wrap round to the bottom, from 0 to 0x007fffff inclusive. So we can detect |
| // a signalling NaN by asking if it's greater than 0xff800000, and a quiet |
| // one by asking if it's less than 0x00800000. |
| uint32_t aadj = (a << 1) + 0x00800000; |
| uint32_t badj = (b << 1) + 0x00800000; |
| if (aadj > 0xff800000) // a is a signalling NaN? |
| return a | 0x00400000; // if so, return it with the quiet bit set |
| if (badj > 0xff800000) // b is a signalling NaN? |
| return b | 0x00400000; // if so, return it with the quiet bit set |
| if (aadj < 0x00800000) // a is a quiet NaN? |
| return a; // if so, return it |
| return b; // otherwise we expect b must be a quiet NaN |
| } |
