12 instruction case-insensitive string equality (for reading booleans)

read.c

int read_bool (char *p)
{
    static const uint64_t true_mask  = 0x00000000ffffffff;
    static const uint64_t true_bits  = 0x0000000065757274;
    static const uint64_t false_mask = 0x000000ffffffffff;
    static const uint64_t false_bits = 0x00000065736c6166;

    static const uint64_t to_lower = 0x2020202020202020;

    uint64_t next8 = *(uint64_t *)p | to_lower;

    int is_true  = (next8 & true_mask) == true_bits;
    int is_false = (next8 & false_mask) == false_bits;

    if (is_true) {
        return 1;
    } else if (is_false) {
        return 0;
    } else {
        return -1;
    }
}

read.s

_read_bool:                             ## @read_bool
	.cfi_startproc
## BB#0:
	pushq	%rbp
Ltmp0:
	.cfi_def_cfa_offset 16
Ltmp1:
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
Ltmp2:
	.cfi_def_cfa_register %rbp
	movabsq	$2314885530818453536, %rcx ## imm = 0x2020202020202020
	orq	(%rdi), %rcx
	movl	$1, %eax
	cmpl	$1702195828, %ecx       ## imm = 0x65757274
	je	LBB0_2
## BB#1:
	movb	$40, %al
	bzhiq	%rax, %rcx, %rax
	xorl	%ecx, %ecx
	movabsq	$435728179558, %rdx     ## imm = 0x65736C6166
	cmpq	%rdx, %rax
	movl	$-1, %eax
	cmovel	%ecx, %eax
LBB0_2:
	popq	%rbp
	retq
	.cfi_endproc