From: Klaus Treichel <ktreichel@web.de>
Date: Sat, 29 Mar 2008 18:45:24 +0000 (+0000)
Subject: Fix signed division of a negative value by a positive power of two on x86.
X-Git-Tag: before.move.to.git~95
X-Git-Url: https://git.unchartedbackwaters.co.uk/w/?a=commitdiff_plain;h=b123eb4c70e5c11bad167025556589a4ed869d42;p=francis%2Flibjit.git

Fix signed division of a negative value by a positive power of two on x86.
---

diff --git a/ChangeLog b/ChangeLog
index 8d49d03..d082236 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-03-29  Klaus treichel  <ktreichel@web.de>
+
+	* jit/jit-rules-x86.ins: Fix signed division of negative values by a
+	constant positive power of two.
+
 2008-03-29  Klaus Treichel  <ktreichel@web.de>
 
 	* jit/jit-apply.c, tools/gen-apply.c: changes to apply needed for
diff --git a/jit/jit-rules-x86.ins b/jit/jit-rules-x86.ins
index 358155a..57fa4a0 100644
--- a/jit/jit-rules-x86.ins
+++ b/jit/jit-rules-x86.ins
@@ -584,13 +584,26 @@ JIT_OP_IDIV: more_space
 		x86_patch(patch, inst);
 		x86_neg_reg(inst, $1);
 	}
-	[reg, imm, if("(((jit_nuint)$2) & (((jit_nuint)$2) - 1)) == 0")] -> {
+	[reg, imm, scratch reg, if("$2 == 2")] -> {
+		x86_mov_reg_reg(inst, $3, $1, 4);
+		x86_shift_reg_imm(inst, X86_SHR, $3, 0x1f);
+		x86_alu_reg_reg(inst, X86_ADD, $1, $3);
+		x86_shift_reg_imm(inst, X86_SAR, $1, 1);
+	}
+	[reg, imm, scratch reg, if("($2 > 0) && (((jit_nuint)$2) & (((jit_nuint)$2) - 1)) == 0")] -> {
 		/* x & (x - 1) is equal to zero if x is a power of 2  */
-		jit_nuint shift, value = $2 >> 1;
+		/* This code is generated by gcc for pentium. */
+		/* We use this code because cmov is not available on all i386 cpus */
+		jit_nuint shift, temp, value = $2 >> 1;
 		for(shift = 0; value; value >>= 1)
 		{
 		    ++shift;
 		}
+		temp = 32 - shift;
+		x86_mov_reg_reg(inst, $3, $1, 4);
+		x86_shift_reg_imm(inst, X86_SAR, $3, 0x1f);
+		x86_shift_reg_imm(inst, X86_SHR, $3, temp);
+		x86_alu_reg_reg(inst, X86_ADD, $1, $3);
 		x86_shift_reg_imm(inst, X86_SAR, $1, shift);
 	}
 	[reg("eax"), imm, scratch reg, scratch reg("edx")] -> {