arch/mips/math-emu/sp_sqrt.c

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

File Facts

System
Linux kernel
Corpus path
arch/mips/math-emu/sp_sqrt.c
Extension
.c
Size
1805 bytes
Lines
104
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 (xs) {
			/* sqrt(-Inf) = Nan */
			ieee754_setcx(IEEE754_INVALID_OPERATION);
			return ieee754sp_indef();
		}
		/* sqrt(+Inf) = Inf */
		return x;

	case IEEE754_CLASS_DNORM:
	case IEEE754_CLASS_NORM:
		if (xs) {
			/* sqrt(-x) = Nan */
			ieee754_setcx(IEEE754_INVALID_OPERATION);
			return ieee754sp_indef();
		}
		break;
	}

	ix = x.bits;

	/* normalize x */
	m = (ix >> 23);
	if (m == 0) {		/* subnormal x */
		for (i = 0; (ix & 0x00800000) == 0; i++)
			ix <<= 1;
		m -= i - 1;
	}
	m -= 127;		/* unbias exponent */
	ix = (ix & 0x007fffff) | 0x00800000;
	if (m & 1)		/* odd m, double x to make it even */
		ix += ix;
	m >>= 1;		/* m = [m/2] */

	/* generate sqrt(x) bit by bit */
	ix += ix;
	s = 0;
	q = 0;			/* q = sqrt(x) */
	r = 0x01000000;		/* r = moving bit from right to left */

	while (r != 0) {
		t = s + r;
		if (t <= ix) {
			s = t + r;
			ix -= t;
			q += r;
		}
		ix += ix;
		r >>= 1;
	}

	if (ix != 0) {
		ieee754_setcx(IEEE754_INEXACT);
		switch (ieee754_csr.rm) {
		case FPU_CSR_RU:
			q += 2;
			break;
		case FPU_CSR_RN:
			q += (q & 1);
			break;
		}
	}
	ix = (q >> 1) + 0x3f000000;
	ix += (m << 23);
	x.bits = ix;
	return x;
}

Annotation

Implementation Notes