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Avoid undefined behavior when shifting in RPN math

--- a/src/asm/rpn.c

+++ b/src/asm/rpn.c

@@ -390,9 +390,9 @@

 		/* Convert the left-hand expression if it's constant */

 		if (src1->isKnown) {

-			uint8_t bytes[] = {RPN_CONST, src1->nVal,

-					   src1->nVal >> 8, src1->nVal >> 16,

-					   src1->nVal >> 24};

+			uint32_t lval = src1->nVal;

+			uint8_t bytes[] = {RPN_CONST, lval, lval >> 8,

+					   lval >> 16, lval >> 24};

 			expr->nRPNPatchSize = sizeof(bytes);

 			expr->tRPN = NULL;

 			expr->nRPNCapacity = 0;

@@ -413,8 +413,9 @@

 		uint32_t patchSize = src2->nRPNPatchSize;

 		/* If the right expression is constant, merge a shim instead */

-		uint8_t bytes[] = {RPN_CONST, src2->nVal, src2->nVal >> 8,

-				   src2->nVal >> 16, src2->nVal >> 24};

+		uint32_t rval = src2->nVal;

+		uint8_t bytes[] = {RPN_CONST, rval, rval >> 8, rval >> 16,

+				   rval >> 24};

 		if (src2->isKnown) {

 			ptr = bytes;

 			len = sizeof(bytes);

@@ -436,7 +437,7 @@

 	*expr = *src;

 	if (rpn_isKnown(expr)) {

-		expr->nVal = expr->nVal >> 8 & 0xFF;

+		expr->nVal = (uint32_t)expr->nVal >> 8 & 0xFF;

 	} else {

 		uint8_t bytes[] = {RPN_CONST,    8, 0, 0, 0, RPN_SHR,

 				   RPN_CONST, 0xFF, 0, 0, 0, RPN_AND};