SQL Server License : Platform Independent
SQL licenses are platform independent which means that if the customer purchases 32-bit license for SQL Server today and later they plan to move to 64-bit; they just need to procure the media and need not purchase new SQL license.
Referring to page 3 of the License Guide available at https://download.microsoft.com/download/6/F/8/6F84A9FE-1E5C-44CC-87BB-C236BFCBA4DF/SQLServer2008_LicensingGuide.pdf
SQL CAL is offered on three platforms (32 bit, 64 bit and IA64). Any SQL CAL (32 bit, 64 bit and IA64) can be used against any licensed SQL Server regardless of the platform (32 bit, 64 bit and IA64).
https://www.microsoft.com/sqlserver/2005/en/us/pricing-licensing-faq.aspx