arch/mips/math-emu/ieee754sp.c

Source file repositories/reference/linux-study-clean/arch/mips/math-emu/ieee754sp.c

File Facts

System
Linux kernel
Corpus path
arch/mips/math-emu/ieee754sp.c
Extension
.c
Size
4349 bytes
Lines
197
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

switch (ieee754_csr.rm) {
		case FPU_CSR_RZ:
			break;
		case FPU_CSR_RN:
			xm += 0x3 + ((xm >> 3) & 1);
			/* xm += (xm&0x8)?0x4:0x3 */
			break;
		case FPU_CSR_RU:	/* toward +Infinity */
			if (!sn)	/* ?? */
				xm += 0x8;
			break;
		case FPU_CSR_RD:	/* toward -Infinity */
			if (sn) /* ?? */
				xm += 0x8;
			break;
		}
	}
	return xm;
}


/* generate a normal/denormal number with over,under handling
 * sn is sign
 * xe is an unbiased exponent
 * xm is 3bit extended precision value.
 */
union ieee754sp ieee754sp_format(int sn, int xe, unsigned int xm)
{
	assert(xm);		/* we don't gen exact zeros (probably should) */

	assert((xm >> (SP_FBITS + 1 + 3)) == 0);	/* no excess */
	assert(xm & (SP_HIDDEN_BIT << 3));

	if (xe < SP_EMIN) {
		/* strip lower bits */
		int es = SP_EMIN - xe;

		if (ieee754_csr.nod) {
			ieee754_setcx(IEEE754_UNDERFLOW);
			ieee754_setcx(IEEE754_INEXACT);

			switch(ieee754_csr.rm) {
			case FPU_CSR_RN:
			case FPU_CSR_RZ:
				return ieee754sp_zero(sn);
			case FPU_CSR_RU:      /* toward +Infinity */
				if (sn == 0)
					return ieee754sp_min(0);
				else
					return ieee754sp_zero(1);
			case FPU_CSR_RD:      /* toward -Infinity */
				if (sn == 0)
					return ieee754sp_zero(0);
				else
					return ieee754sp_min(1);
			}
		}

		if (xe == SP_EMIN - 1 &&
		    ieee754sp_get_rounding(sn, xm) >> (SP_FBITS + 1 + 3))
		{
			/* Not tiny after rounding */
			ieee754_setcx(IEEE754_INEXACT);
			xm = ieee754sp_get_rounding(sn, xm);
			xm >>= 1;
			/* Clear grs bits */
			xm &= ~(SP_MBIT(3) - 1);
			xe++;
		} else {
			/* sticky right shift es bits
			 */
			xm = XSPSRS(xm, es);
			xe += es;
			assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
			assert(xe == SP_EMIN);
		}
	}
	if (xm & (SP_MBIT(3) - 1)) {
		ieee754_setcx(IEEE754_INEXACT);
		if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
			ieee754_setcx(IEEE754_UNDERFLOW);
		}

		/* inexact must round of 3 bits
		 */
		xm = ieee754sp_get_rounding(sn, xm);
		/* adjust exponent for rounding add overflowing
		 */
		if (xm >> (SP_FBITS + 1 + 3)) {
			/* add causes mantissa overflow */

Annotation

Implementation Notes