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| author | Michael Sevakis <jethead71@rockbox.org> | 2017-09-07 15:41:52 -0400 |
|---|---|---|
| committer | Michael Sevakis <jethead71@rockbox.org> | 2017-09-07 15:45:55 -0400 |
| commit | c6d5cd74a866901eb8f6e69e642f617e5810e0c6 (patch) | |
| tree | bfa16a09051e0d7f0298575d3f5b34bcf33d9cf3 /lib/arm_support/support-arm.S | |
| parent | 28591f2e92cff7edb8da4339b61b15305419863a (diff) | |
ARM support: provide compiler a better popcount function
Just the 32-bit one for now. The default uses lookup tables and is
ungainly and bloated.
Change-Id: I4a2eb31defb1f4d6f6853b65fe6dacc380d6ffc0
Diffstat (limited to 'lib/arm_support/support-arm.S')
| -rw-r--r-- | lib/arm_support/support-arm.S | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/lib/arm_support/support-arm.S b/lib/arm_support/support-arm.S index 6141a3f158..df49dc49e8 100644 --- a/lib/arm_support/support-arm.S +++ b/lib/arm_support/support-arm.S @@ -701,3 +701,34 @@ __aeabi_idivmod: .byte 0x92, 0x90, 0x8f, 0x8e, 0x8d, 0x8c, 0x8a, 0x89 .byte 0x88, 0x87, 0x86, 0x85, 0x84, 0x83, 0x82, 0x81 #endif + +/* + * int __popcountsi2(unsigned int x) + * int __popcountdi2(unsigned long x) + */ + .section .text.__popcountsi2, "ax", %progbits + .global __popcountsi2 + .type __popcountsi2, %function + .global __popcountdi2 + .type __popcountdi2, %function + .set __popcountdi2, __popcountsi2 +__popcountsi2: + mov r1, #0x33 @ r1 = 0x33333333 + orr r1, r1, r1, lsl #8 @ ... + orr r1, r1, r1, lsl #16 @ ... + eor r2, r1, r1, lsl #1 @ r2 = 0x55555555 + and r2, r2, r0, lsr #1 @ r2 = (x >> 1) & 0x55555555 + sub r0, r0, r2 @ x = x - ((x >> 1) & 0x55555555) + and r2, r1, r0 @ r2 = x & 0x33333333 + and r1, r1, r0, lsr #2 @ r1 = (x >> 2) & 0x33333333 + add r0, r2, r1 @ x = (x & 0x33333333) + ((x >> 2) & 0x33333333) + mov r1, #0x0f @ r1 = 0x0f0f0f0f + orr r1, r1, r1, lsl #8 @ ... + orr r1, r1, r1, lsl #16 @ ... + add r0, r0, lsr #4 @ x = x + (x >> 4) + and r0, r0, r1 @ x = (x + (x >> 4)) & 0x0f0f0f0f + add r0, r0, lsr #16 @ x = x + (x >> 16) + add r0, r0, lsr #8 @ x = x + (x >> 8) + and r0, r0, #0x3f @ x &= 0x3f + bx lr @ return x + .size __popcountsi2, .-__popcountsi2 |