Extension B: fix ctz instruction IDL code (#471)

ayosher · web-flow · commit f5d220143c4e · 2025-03-06T19:50:56.000Z
* Extension B: fix ctz instruction IDL code

Signed-off-by: Albert Yosher &lt;quic_ayosher@quicinc.com&gt;

* B extension: fixing ctz and ctzw instructions

Signed-off-by: Albert Yosher &lt;quic_ayosher@quicinc.com&gt;

* B extensions: additional fix for ctz instruction to support case when xlen() != XLEN

Signed-off-by: Albert Yosher &lt;quic_ayosher@quicinc.com&gt;

---------

Signed-off-by: Albert Yosher &lt;quic_ayosher@quicinc.com&gt;
diff --git a/arch/inst/B/ctz.yaml b/arch/inst/B/ctz.yaml
@@ -30,7 +30,11 @@ operation(): |
     raise (ExceptionCode::IllegalInstruction, mode(), $encoding);
   }
 
-  X[rd] = (xlen() - 1) - $signed(lowest_set_bit(X[rs1]));
+  if (xlen() == 32) {
+    X[rd] = lowest_set_bit(X[rs1][31:0]);
+  } else {
+    X[rd] = lowest_set_bit(X[rs1]);
+  }
 
 sail(): |
   {
diff --git a/arch/inst/B/ctzw.yaml b/arch/inst/B/ctzw.yaml
@@ -31,7 +31,7 @@ operation(): |
     raise (ExceptionCode::IllegalInstruction, mode(), $encoding);
   }
 
-  X[rd] = (xlen() - 1) - $signed(lowest_set_bit(X[rs1][31:0]));
+  X[rd] = lowest_set_bit(X[rs1][31:0]);
 
 sail(): |
   {

Original file line number	Diff line number	Diff line change
`@@ -30,7 +30,11 @@ operation(): \|`
`30`	`30`	`raise (ExceptionCode::IllegalInstruction, mode(), $encoding);`
`31`	`31`	`}`
`32`	`32`
`33`		`- X[rd] = (xlen() - 1) - $signed(lowest_set_bit(X[rs1]));`
	`33`	`+ if (xlen() == 32) {`
	`34`	`+ X[rd] = lowest_set_bit(X[rs1][31:0]);`
	`35`	`+ } else {`
	`36`	`+ X[rd] = lowest_set_bit(X[rs1]);`
	`37`	`+ }`
`34`	`38`
`35`	`39`	`sail(): \|`
`36`	`40`	`{`
Original file line number	Diff line number	Diff line change
`@@ -31,7 +31,7 @@ operation(): \|`
`31`	`31`	`raise (ExceptionCode::IllegalInstruction, mode(), $encoding);`
`32`	`32`	`}`
`33`	`33`
`34`		`- X[rd] = (xlen() - 1) - $signed(lowest_set_bit(X[rs1][31:0]));`
	`34`	`+ X[rd] = lowest_set_bit(X[rs1][31:0]);`
`35`	`35`
`36`	`36`	`sail(): \|`
`37`	`37`	`{`