arch/mips/math-emu/sp_maddf.c

Source file repositories/reference/linux-study-clean/arch/mips/math-emu/sp_maddf.c

File Facts

System
Linux kernel
Corpus path
arch/mips/math-emu/sp_maddf.c
Extension
.c
Size
6564 bytes
Lines
279
Domain
Architecture Layer
Bucket
arch/mips
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

if ((zc == IEEE754_CLASS_INF) && (zs != rs)) {
			/*
			 * Cases of addition of infinities with opposite signs
			 * or subtraction of infinities with same signs.
			 */
			ieee754_setcx(IEEE754_INVALID_OPERATION);
			return ieee754sp_indef();
		}
		/*
		 * z is here either not an infinity, or an infinity having the
		 * same sign as product (x*y). The result must be an infinity,
		 * and its sign is determined only by the sign of product (x*y).
		 */
		return ieee754sp_inf(rs);

	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
		if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		if (zc == IEEE754_CLASS_ZERO) {
			/* Handle cases +0 + (-0) and similar ones. */
			if (zs == rs)
				/*
				 * Cases of addition of zeros of equal signs
				 * or subtraction of zeroes of opposite signs.
				 * The sign of the resulting zero is in any
				 * such case determined only by the sign of z.
				 */
				return z;

			return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
		}
		/* x*y is here 0, and z is not 0, so just return z */
		return z;

	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
		SPDNORMX;
		fallthrough;
	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
		if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		SPDNORMY;
		break;

	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
		if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		SPDNORMX;
		break;

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
		if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		/* continue to real computations */
	}

	/* Finally get to do some computation */

	/*
	 * Do the multiplication bit first
	 *
	 * rm = xm * ym, re = xe + ye basically
	 *
	 * At this point xm and ym should have been normalized.
	 */

	/* rm = xm * ym, re = xe+ye basically */
	assert(xm & SP_HIDDEN_BIT);
	assert(ym & SP_HIDDEN_BIT);

	re = xe + ye;

	/* Multiple 24 bit xm and ym to give 48 bit results */
	rm64 = (uint64_t)xm * ym;

	/* Shunt to top of word */
	rm64 = rm64 << 16;

	/* Put explicit bit at bit 62 if necessary */
	if ((int64_t) rm64 < 0) {
		rm64 = rm64 >> 1;
		re++;
	}

	assert(rm64 & (1 << 62));

	if (zc == IEEE754_CLASS_ZERO) {

Annotation

Implementation Notes