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Floating-point in Linux Kernel

http://porterchen-note.blogspot.com/2011/03/linux-kernel-and-floating-point.html

/* 
 * Goal here is to save needless saving/storing the NEON context at each task switch for the NEON, lightly said,
 * not being used by that often by the tasks. To serve it: 
 * - for each userland task having NEON register file used we keep a track of what CPU it used before it
 *  got switched out. If NULL then it was a kernel
 * - for each CPU (per-cpu) we store what task used the NEON register file 
 * 
 * If the two are in sync/ yield the same then we go saving/storing the context. If not we ignore it.
 * 
 * Kernel is treated differently here as while in NEON preemption and interrupts are off. As a result
 * it mustn't sleep while there. 
 *
 */
kernel_neon_begin();                       
xor_block_neon_inner.do_2(bytes, p1, p2);  
kernel_neon_end();                         

Set/clear bit

#define NTH_BIT 4                                                              
                                                                               
unsigned int addr = 0xffffffff;                                        
enum flags { clear, set };                                             
                                                                               
addr &= ~(1<<NTH_BIT);                                                 
printf("mb: clearing %dth bit %x of %x\n", NTH_BIT, addr, 0xffffffff); 
                                                                               
addr |= (1<<NTH_BIT);                                                  
printf("mb: setting %dth bit %x\n", NTH_BIT, addr);