1 files changed, 125 insertions, 0 deletions
diff --git a/lib/i386/umoddi3.S b/lib/i386/umoddi3.S
new file mode 100644
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+++ b/lib/i386/umoddi3.S
@@ -0,0 +1,125 @@
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+
+#include "../assembly.h"
+
+// du_int __umoddi3(du_int a, du_int b);
+
+// result = remainder of a / b.
+// both inputs and the output are 64-bit unsigned integers.
+// This will do whatever the underlying hardware is set to do on division by zero.
+// No other exceptions are generated, as the divide cannot overflow.
+//
+// This is targeted at 32-bit x86 *only*, as this can be done directly in hardware
+// on x86_64.  The performance goal is ~40 cycles per divide, which is faster than
+// currently possible via simulation of integer divides on the x87 unit.
+//
+
+// Stephen Canon, December 2008
+
+#ifdef __i386__
+
+.text
+.align 4
+DEFINE_COMPILERRT_FUNCTION(__umoddi3)
+
+	pushl		%ebx
+	movl	 20(%esp),			%ebx	// Find the index i of the leading bit in b.
+	bsrl		%ebx,			%ecx	// If the high word of b is zero, jump to
+	jz			9f						// the code to handle that special case [9].
+	
+	/* High word of b is known to be non-zero on this branch */
+	
+	movl	 16(%esp),			%eax	// Construct bhi, containing bits [1+i:32+i] of b
+	
+	shrl		%cl,			%eax	// Practically, this means that bhi is given by:
+	shrl		%eax					//
+	notl		%ecx					//		bhi = (high word of b) << (31 - i) |
+	shll		%cl,			%ebx	//			  (low word of b) >> (1 + i)
+	orl			%eax,			%ebx	//
+	movl	 12(%esp),			%edx	// Load the high and low words of a, and jump
+	movl	  8(%esp),			%eax	// to [2] if the high word is larger than bhi
+	cmpl		%ebx,			%edx	// to avoid overflowing the upcoming divide.
+	jae			2f						
+		
+	/* High word of a is greater than or equal to (b >> (1 + i)) on this branch */
+	
+	divl		%ebx					// eax <-- qs, edx <-- r such that ahi:alo = bs*qs + r
+
+	pushl		%edi
+	notl		%ecx
+	shrl		%eax
+	shrl		%cl,			%eax	// q = qs >> (1 + i)
+	movl		%eax,			%edi
+	mull	 20(%esp)					// q*blo
+	movl	 12(%esp),			%ebx
+	movl	 16(%esp),			%ecx	// ECX:EBX = a
+	subl		%eax,			%ebx
+	sbbl		%edx,			%ecx	// ECX:EBX = a - q*blo
+	movl	 24(%esp),			%eax
+	imull		%edi,			%eax	// q*bhi
+	subl		%eax,			%ecx	// ECX:EBX = a - q*b
+	
+	jnc			1f						// if positive, this is the result.
+	addl	 20(%esp),			%ebx	// otherwise
+	adcl	 24(%esp),			%ecx	// ECX:EBX = a - (q-1)*b = result
+1:	movl		%ebx,			%eax
+	movl		%ecx,			%edx
+	
+	popl		%edi
+	popl		%ebx
+	retl
+
+
+2:	/* High word of a is greater than or equal to (b >> (1 + i)) on this branch */
+	 
+	subl		%ebx,			%edx	// subtract bhi from ahi so that divide will not
+	divl		%ebx					// overflow, and find q and r such that
+										//
+										//		ahi:alo = (1:q)*bhi + r
+										//
+										// Note that q is a number in (31-i).(1+i)
+										// fix point.
+
+	pushl		%edi
+	notl		%ecx
+	shrl		%eax
+	orl			$0x80000000,	%eax
+	shrl		%cl,			%eax	// q = (1:qs) >> (1 + i)
+	movl		%eax,			%edi
+	mull	 20(%esp)					// q*blo
+	movl	 12(%esp),			%ebx
+	movl	 16(%esp),			%ecx	// ECX:EBX = a
+	subl		%eax,			%ebx
+	sbbl		%edx,			%ecx	// ECX:EBX = a - q*blo
+	movl	 24(%esp),			%eax
+	imull		%edi,			%eax	// q*bhi
+	subl		%eax,			%ecx	// ECX:EBX = a - q*b
+
+	jnc			3f						// if positive, this is the result.
+	addl	 20(%esp),			%ebx	// otherwise
+	adcl	 24(%esp),			%ecx	// ECX:EBX = a - (q-1)*b = result
+3:	movl		%ebx,			%eax
+	movl		%ecx,			%edx
+	
+	popl		%edi
+	popl		%ebx
+	retl
+
+
+	
+9:	/* High word of b is zero on this branch */
+
+	movl	 12(%esp),			%eax	// Find qhi and rhi such that
+	movl	 16(%esp),			%ecx	//
+	xorl		%edx,			%edx	//		ahi = qhi*b + rhi	with	0 ≤ rhi < b
+	divl		%ecx					//
+	movl		%eax,			%ebx	//
+	movl	  8(%esp),			%eax	// Find rlo such that
+	divl		%ecx					//
+	movl		%edx,			%eax	//		rhi:alo = qlo*b + rlo  with 0 ≤ rlo < b
+	popl		%ebx					//
+	xorl		%edx,			%edx	// and return 0:rlo
+	retl								// 
+	
+#endif // __i386__