From: David Gow <david@ingeniumdigital.com>
Date: Sat, 5 Jul 2014 16:32:16 +0000 (+0800)
Subject: This might help: divide an arbint by a uint64
X-Git-Url: https://git.ucc.asn.au/?a=commitdiff_plain;h=b0561967639ff158020b334433ac481a082480cc;p=ipdf%2Fcode.git

This might help: divide an arbint by a uint64
---

diff --git a/src/div_digits_asm.s b/src/div_digits_asm.s
new file mode 100644
index 0000000..b11dd92
--- /dev/null
+++ b/src/div_digits_asm.s
@@ -0,0 +1,28 @@
+.section .text
+.globl div_digits
+.type div_digits, @function
+
+# div_digits(digits, div, size, res, rem)
+# divides an arbint in digits by uint64 div into res with remainder rem
+# Either res or rem may alias digits
+# digits = rdi, div = rsx, size = rdx, res = rcx, rem = r8
+div_digits:
+	movq %rdx, %r9
+	leaq -8(%rdi,%r9,8), %rdi	# We want to point to the end of the buffer (LSB)
+	leaq -8(%rcx,%r9,8), %rcx	# We want to point to the end of the buffer (LSB)
+	leaq -8(%r8,%r9,8), %r8		# We want to point to the end of the buffer (LSB)
+	movq $0, %rdx
+loop:
+	movq (%rdi), %rax
+	divq %rsi			# rdx:rax/rsi => rax, rdx:rax%rsi => rdx
+	movq %rax, (%rcx)
+	movq %rdx, (%r8)
+	dec %r9
+	leaq -8(%rdi), %rdi
+	leaq -8(%rcx), %rcx
+	leaq -8(%r8), %r8
+	jnz loop
+end:
+	ret
+	
+