arch/parisc/math-emu/sfsqrt.c

Source file repositories/reference/linux-study-clean/arch/parisc/math-emu/sfsqrt.c

File Facts

System
Linux kernel
Corpus path
arch/parisc/math-emu/sfsqrt.c
Extension
.c
Size
4165 bytes
Lines
175
Domain
Architecture Layer
Bucket
arch/parisc
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 ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
                /*
                 * is signaling NaN?
                 */
                if (Sgl_isone_signaling(src)) {
                        /* trap if INVALIDTRAP enabled */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                        /* make NaN quiet */
                        Set_invalidflag();
                        Sgl_set_quiet(src);
                }
                /*
                 * Return quiet NaN or positive infinity.
		 *  Fall through to negative test if negative infinity.
                 */
		if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
                	*dstptr = src;
                	return(NOEXCEPTION);
		}
        }

        /*
         * check for zero source operand
         */
	if (Sgl_iszero_exponentmantissa(src)) {
		*dstptr = src;
		return(NOEXCEPTION);
	}

        /*
         * check for negative source operand 
         */
	if (Sgl_isone_sign(src)) {
		/* trap if INVALIDTRAP enabled */
		if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
		/* make NaN quiet */
		Set_invalidflag();
		Sgl_makequietnan(src);
		*dstptr = src;
		return(NOEXCEPTION);
	}

	/*
	 * Generate result
	 */
	if (src_exponent > 0) {
		even_exponent = Sgl_hidden(src);
		Sgl_clear_signexponent_set_hidden(src);
	}
	else {
		/* normalize operand */
		Sgl_clear_signexponent(src);
		src_exponent++;
		Sgl_normalize(src,src_exponent);
		even_exponent = src_exponent & 1;
	}
	if (even_exponent) {
		/* exponent is even */
		/* Add comment here.  Explain why odd exponent needs correction */
		Sgl_leftshiftby1(src);
	}
	/*
	 * Add comment here.  Explain following algorithm.
	 * 
	 * Trust me, it works.
	 *
	 */
	Sgl_setzero(result);
	newbit = 1 << SGL_P;
	while (newbit && Sgl_isnotzero(src)) {
		Sgl_addition(result,newbit,sum);
		if(sum <= Sgl_all(src)) {
			/* update result */
			Sgl_addition(result,(newbit<<1),result);
			Sgl_subtract(src,sum,src);
		}
		Sgl_rightshiftby1(newbit);
		Sgl_leftshiftby1(src);
	}
	/* correct exponent for pre-shift */
	if (even_exponent) {
		Sgl_rightshiftby1(result);
	}

	/* check for inexact */
	if (Sgl_isnotzero(src)) {
		if (!even_exponent && Sgl_islessthan(result,src)) 
			Sgl_increment(result);
		guardbit = Sgl_lowmantissa(result);
		Sgl_rightshiftby1(result);

Annotation

Implementation Notes