u32 __vfp_single_normaliseround()

in vfp/vfpsingle.c [70:208]

• 93 lines of code
• 21 McCabe index (conditional complexity)

u32 __vfp_single_normaliseround(int sd, struct vfp_single *vs, u32 fpscr, u32 exceptions)
#else
u32 vfp_single_normaliseround(int sd, struct vfp_single *vs, u32 fpscr, u32 exceptions, const char *func)
#endif
{
	u32 significand, incr, rmode;
	int exponent, shift, underflow;

	vfp_single_dump("pack: in", vs);

	/*
	 * Infinities and NaNs are a special case.
	 */
	if (vs->exponent == 255 && (vs->significand == 0 || exceptions))
		goto pack;

	/*
	 * Special-case zero.
	 */
	if (vs->significand == 0) {
		vs->exponent = 0;
		goto pack;
	}

	exponent = vs->exponent;
	significand = vs->significand;

	/*
	 * Normalise first.  Note that we shift the significand up to
	 * bit 31, so we have VFP_SINGLE_LOW_BITS + 1 below the least
	 * significant bit.
	 */
	shift = 32 - fls(significand);
	if (shift < 32 && shift) {
		exponent -= shift;
		significand <<= shift;
	}

#ifdef DEBUG
	vs->exponent = exponent;
	vs->significand = significand;
	vfp_single_dump("pack: normalised", vs);
#endif

	/*
	 * Tiny number?
	 */
	underflow = exponent < 0;
	if (underflow) {
		significand = vfp_shiftright32jamming(significand, -exponent);
		exponent = 0;
#ifdef DEBUG
		vs->exponent = exponent;
		vs->significand = significand;
		vfp_single_dump("pack: tiny number", vs);
#endif
		if (!(significand & ((1 << (VFP_SINGLE_LOW_BITS + 1)) - 1)))
			underflow = 0;
	}

	/*
	 * Select rounding increment.
	 */
	incr = 0;
	rmode = fpscr & FPSCR_RMODE_MASK;

	if (rmode == FPSCR_ROUND_NEAREST) {
		incr = 1 << VFP_SINGLE_LOW_BITS;
		if ((significand & (1 << (VFP_SINGLE_LOW_BITS + 1))) == 0)
			incr -= 1;
	} else if (rmode == FPSCR_ROUND_TOZERO) {
		incr = 0;
	} else if ((rmode == FPSCR_ROUND_PLUSINF) ^ (vs->sign != 0))
		incr = (1 << (VFP_SINGLE_LOW_BITS + 1)) - 1;

	pr_debug("VFP: rounding increment = 0x%08x\n", incr);

	/*
	 * Is our rounding going to overflow?
	 */
	if ((significand + incr) < significand) {
		exponent += 1;
		significand = (significand >> 1) | (significand & 1);
		incr >>= 1;
#ifdef DEBUG
		vs->exponent = exponent;
		vs->significand = significand;
		vfp_single_dump("pack: overflow", vs);
#endif
	}

	/*
	 * If any of the low bits (which will be shifted out of the
	 * number) are non-zero, the result is inexact.
	 */
	if (significand & ((1 << (VFP_SINGLE_LOW_BITS + 1)) - 1))
		exceptions |= FPSCR_IXC;

	/*
	 * Do our rounding.
	 */
	significand += incr;

	/*
	 * Infinity?
	 */
	if (exponent >= 254) {
		exceptions |= FPSCR_OFC | FPSCR_IXC;
		if (incr == 0) {
			vs->exponent = 253;
			vs->significand = 0x7fffffff;
		} else {
			vs->exponent = 255;		/* infinity */
			vs->significand = 0;
		}
	} else {
		if (significand >> (VFP_SINGLE_LOW_BITS + 1) == 0)
			exponent = 0;
		if (exponent || significand > 0x80000000)
			underflow = 0;
		if (underflow)
			exceptions |= FPSCR_UFC;
		vs->exponent = exponent;
		vs->significand = significand >> 1;
	}

 pack:
	vfp_single_dump("pack: final", vs);
	{
		s32 d = vfp_single_pack(vs);
#ifdef DEBUG
		pr_debug("VFP: %s: d(s%d)=%08x exceptions=%08x\n", func,
			 sd, d, exceptions);
#endif
		vfp_put_float(d, sd);
	}

	return exceptions;
}